boards: beagle: pocketbeagle_2: Add MSPM0 support

PocketBeagle 2 contains an MSPM0L1105 soc which emulates ADC and EEPROM.
It is connected to the AM62xx soc over I2C and SPI.

The initial support just allows building the minimal zephyr sample. Due
to the constraints and the purpose of the SOC, most peripherals should
not be enabled in the main dts.

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