boards: beagle: Add PocketBeagle 2 M4 support

Add initial support for the PocketBeagle 2 MCU domain Cortex-M4F core.
This only adds support for A0 revision (i.e. the version with AM6232).

PocketBeagle 2: https://www.beagleboard.org/boards/pocketbeagle-2



Signed-off-by: Ayush Singh <ayush@beagleboard.org>