board_get_px4_guid() called board_get_uuid() with a 2 bytes offset into an
uint8_t array. This gives no guarantees on alignment, and board_get_uuid()
casts it to an uint32_t array, leading to potentially unaligned accesses.

Just to make sure we never have an UUID == 0

   This file was clearly clearly but built.

   This common code can be used byt posix based boars to provide
   the board_identity API.