boards: arm64: Add PHYTEC phyCORE-AM62x A53 board support

PHYTEC phyCORE-AM62x is board is based on TI Sitara applications
processor, composed of a quad Cortex®-A53 cluster and a single
Cortex®-M4 core.

Zephyr OS is ported to run on the Cortex®-A53 core.

Signed-off-by: Grant Ramsay <gramsay@enphaseenergy.com>