These two boards are used for testing, so it is favorable to have them
added early.
The full test set is:
- ADAFRUIT_FEATHER_M4_EXPRESS: SAMD51 with 32kHz crystal.
- ADAFRUIT_ITSYBITSY_M0_EXPRESS: SAMD21 without crystal.
- ADAFRUIT_ITSYBITSY_M4_EXPRESS: SAMD51 without crystal.
- SEEED_XIAO: SAM21 with 32kHz crystal.
