puf_sram only relies on an uninitialized chunk of memory.
This means to enable it we just have to hook up puf_sram_init().
All memory after __bss_end should be uninitialized at startup, so
just use that.
- split up interrupt vector code from bootloader.c to vectors.c
- moved bootloader.c to arm7_init.c
- Use consistent naming:
- use lower case for everything but preprocessor stuff
- ISRs now named isr_foo()