19733: cpu/msp430: reorganize code r=maribu a=maribu
### Contribution description
RIOT supports two distinct families of the MSP430: The [MSP430 x1xx] MCU family and the [MSP430 F2xx/G2xx] MCU family. For both incompatible MCU families the code was located in the msp430fxyz folder, resulting in case of the UART driver in particularly bizarre code looking roughly like this:
```C
#ifndef UART_USE_USCI
/* implementation of x1xx peripheral ... */
#else
/* implementation of F2xx/G2xx peripheral ... */
#endif
/* zero shared code between both variants */
```
This moves peripheral drivers shared between the two families to msp430_common and splits the SPI and UART driver into two MCU families.
In addition, it cleans up the `msp430_regs.h` by dropping most of it and using the macros and symbols provided by the vendor header files. There is little reason for us to maintain constants when TI is already doing that.
[MSP430 x1xx]: https://www.ti.com/lit/ug/slau049f/slau049f.pdf
[MSP430 F2xx/G2xx]: https://www.ti.com/lit/ug/slau144k/slau144k.pdf
19747: gnrc/ipv6/nib: reset rs_sent counter also for not-6LN interfaces r=maribu a=fabian18
19769: cpu/nrf53: add initial support with nRF5340DK-APP board r=maribu a=dylad
### Contribution description
This PR adds support for nRF5340 MCU and its associated Nordic development board, nRF5340DK.
This MCU provides a dual Cortex-M33, one application core running at up to 128MHz, and one network core running at up to 64MHz.
Peripherals are inherited from others Nordic MCUs families so it shouldn't be hard to add more of them in followup PRs.
For now, only the minimal set of peripherals is supported:
- GPIO / GPIO_IRQ
- UART
- TIMER
### Testing procedure
Build the usual test application for the supported peripherals and flash the board.
nRF5340DK provides two serial ports on its embedded debugger. RIOT's shell should be available on the first one (/dev/ttyACM0)
### Issues/PRs references
#18576#19267
19782: cpu/msp430: fix for ti's msp430-gcc-opensource package ld version r=maribu a=hugueslarrive
### Contribution description
My msp430 toolchain (https://www.ti.com/tool/MSP430-GCC-OPENSOURCE) was broken by #19484:
```
hugues@p700:~/github/cpu_msp430_common/RIOT$ BOARD=msb-430 make -j64 -C examples/hello-world
make : on entre dans le répertoire « /home/hugues/github/cpu_msp430_common/RIOT/examples/hello-world »
Building application "hello-world" for "msb-430" with MCU "msp430fxyz".
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/boards/common/init
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/boards/msb-430
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/core
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/core/lib
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430fxyz
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/drivers
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/boards/common/msb-430
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/drivers/periph_common
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/auto_init
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/div
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/libc
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/malloc_thread_safe
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430_common
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/newlib_syscalls_default
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430fxyz/periph
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/preprocessor
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/stdio_uart
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430_common/periph
/opt/ti/msp430-gcc/bin/../lib/gcc/msp430-elf/9.3.1/../../../../msp430-elf/bin/ld: .rodata not found for insert
collect2: error: ld returned 1 exit status
make: *** [/home/hugues/github/cpu_msp430_common/RIOT/examples/hello-world/../../Makefile.include:761 : /home/hugues/github/cpu_msp430_common/RIOT/examples/hello-world/bin/msb-430/hello-world.elf] Erreur 1
make : on quitte le répertoire « /home/hugues/github/cpu_msp430_common/RIOT/examples/hello-world »
hugues@p700:~/github/cpu_msp430_common/RIOT$ /opt/ti/msp430-gcc/msp430-elf/bin/ld --version
GNU ld (Mitto Systems Limited - msp430-gcc 9.3.1.11) 2.34
Copyright (C) 2020 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty.
hugues@p700:~/github/cpu_msp430_common/RIOT$ /opt/ti/msp430-gcc/msp430-elf/bin/ld --version | grep -Eo '[0-9]\.[0-9]+'
9.3
1.11
2.34
hugues@p700:~/github/cpu_msp430_common/RIOT$ /opt/ti/msp430-gcc/msp430-elf/bin/ld --version | grep -Eo '[0-9]\.[0-9]+$'
2.34
```
### Testing procedure
```
hugues@p700:~/github/cpu_msp430_common/RIOT$ BOARD=msb-430 make -j64 -C examples/hello-world
make : on entre dans le répertoire « /home/hugues/github/cpu_msp430_common/RIOT/examples/hello-world »
Building application "hello-world" for "msb-430" with MCU "msp430fxyz".
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/boards/common/init
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/boards/msb-430
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/core
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/core/lib
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430fxyz
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/drivers
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/boards/common/msb-430
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/drivers/periph_common
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/auto_init
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/div
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/libc
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/malloc_thread_safe
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/newlib_syscalls_default
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/preprocessor
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430_common
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/sys/stdio_uart
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430fxyz/periph
"make" -C /home/hugues/github/cpu_msp430_common/RIOT/cpu/msp430_common/periph
text data bss dec hex filename
8612 722 866 10200 27d8 /home/hugues/github/cpu_msp430_common/RIOT/examples/hello-world/bin/msb-430/hello-world.elf
make : on quitte le répertoire « /home/hugues/github/cpu_msp430_common/RIOT/examples/hello-world »
```
### Issues/PRs references
Introduced by #19484, highlighted in #16727.
Co-authored-by: Marian Buschsieweke <marian.buschsieweke@posteo.net>
Co-authored-by: Fabian Hüßler <fabian.huessler@ml-pa.com>
Co-authored-by: Dylan Laduranty <dylan.laduranty@mesotic.com>
Co-authored-by: Hugues Larrive <hlarrive@pm.me>
This avoids a race condition where the default router slots for the 6LBR
are used up by router advertisements from the 6Lo network that arrived
before router advertisements from the upstream network.
The border router should ignore 'default routers' from the 6Lo network as
it consitutes the uplink for that network.
If multihop distribution is not done using RA messages, then the
routers follow [RFC4861], which states that they merely do some
consistency checks; in this case, nothing in Section 8.1 applies.
- https://datatracker.ietf.org/doc/html/rfc6775#section-8.1
If the fib contains a route to a subnet via another host, it can not
be on-link.
Consider fib entries when deciding whether an address is on-link.
If a route via another host is a stronger match than an on-link
prefix, the address must be off-link.
When the default router was removed or could not be added, `dr` will
be NULL.
In this case, don't cease sending router solicitations - we still don't
have a default router.
