arm64: dts: rockchip: add basic dts for the radxa rock3 model a

Add basic device tree for the Radxa ROCK3 Model A board (with
the Rockchip RK3568 SoC) including Ethernet, USB2 and headphone
connector.

Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Link: https://lore.kernel.org/r/20220310210352.451136-3-michael.riesch@wolfvision.net


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