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

arch/arm64/boot/dts/rockchip/Makefile

@@ -61,3 +61,4 @@ dtb-$(CONFIG_ARCH_ROCKCHIP) += rk3566-pinenote-v1.2.dtb
 dtb-$(CONFIG_ARCH_ROCKCHIP) += rk3566-quartz64-a.dtb
 dtb-$(CONFIG_ARCH_ROCKCHIP) += rk3568-bpi-r2-pro.dtb
 dtb-$(CONFIG_ARCH_ROCKCHIP) += rk3568-evb1-v10.dtb
+dtb-$(CONFIG_ARCH_ROCKCHIP) += rk3568-rock-3a.dtb