arm64: dts: rockchip: Add support for NanoPi R6S

Add basic NanoPi R6S support that comes with USB2, PCIe, SD card, eMMC
support.

Signed-off-by: Muhammed Efe Cetin <efectn@protonmail.com>
Link: https://lore.kernel.org/r/6db3b653efc6f0a2dca8e96fdd0503906db72fb6.1703934548.git.efectn@protonmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>