soc: amd: Add initial support for Versal Net SoC APU (Cortex-A78)

Add initial support for the Versal Net SoC APU, which is based on
the Arm Cortex-A78 processor. It includes basic wiring for memory
regions, UART, interrupt controller, and timer.

The versalnet_apu.dtsi file defines peripherals shared across the SoC,
while versalnet_a78.dtsi captures peripherals private to the Cortex-A78
processor. These device trees lay the groundwork for further APU-based
development on the Versal Net platform.

Signed-off-by: Appana Durga Kedareswara rao <appana.durga.kedareswara.rao@amd.com>