arm64: dts: rockchip: Add rock-5a board

Add board file for the RK3588s Rock 5A board. While the hardware
offers plenty of peripherals and connectivity this basic implementation
just handles things required to access eMMC, UART and Ethernet (i.e.
enough to successfully boot Linux).

Reviewed-by: Michael Riesch <michael.riesch@wolfvision.net>
Tested-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20230109155801.51642-7-sebastian.reichel@collabora.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>