arm64: rk3399: Add support NanoPi R4s

arm64: rk3399: Add support NanoPi R4s

NanoPi R4s is SBC base on Rockchip RK3399 hexa-core processor with
dual-Core Cortex-A72 and Mali-T864 GPU with 4GiB(LPDDR4) of RAM, SD card support,
including 2 gigabit ethernet(RTL8211E 1Gbps - RTL8111H 1Gbps) and 2 USB 3.0 port.
port.It also has two GPIO headers which allows further peripherals to be used.

The devicetree file is taken of the rk3399 nanopi4 Linux kernel [1].

[1] https://github.com/torvalds/linux/commit/e7a095908227fb3ccc86d001d9e13c9ae2bef8e6

Signed-off-by: xiaobo <peterwillcn@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>