boards: beagle: pocketbeagle_2: a53: Enable PSCI

Use both cores for Zephyr by default. I did enable SMP, however forgot
to enable PSCI to turn on the other cores in the initial PR.

Tested with samples: `tests/arch/arm64/arm64_psci/` and
`samples/arch/smp/pi`

Requires [0].

[0]: https://github.com/zephyrproject-rtos/zephyr/pull/95325



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