This fixes a race in `LED<NUM>_TOGGLE`, which is a read-copy-write
operation. Any access to a GPIO pin on the same GPIO port that
happens concurrently could result in data corruption. Using the
GPIO LL API, which is thread-safe, fixes the issue.
Note: The used GPIO LL functions will work even in when the GPIO LL
module is not used.
LED LD1 has no special function on the board STM32F746-DISCO and therefore can be used freely. This LED is also defined as ARDUINO LED pin D13 in the schematic.
