arm64: dts: rockchip: Add devicetree for the FriendlyElec NanoPi R76S

arm64: dts: rockchip: Add devicetree for the FriendlyElec NanoPi R76S

The NanoPi R76S (as "R76S") is an open-sourced mini IoT gateway
device with two 2.5G, designed and developed by FriendlyElec.

Specification:
- Rockchip RK3576
- 2/4GB LPDDR4X RAM
- 2x 2500Base-T (PCIe, rtl8125b)
- 3x LEDs (Power, LAN, WAN)
- 32GB eMMC
- MicroSD Slot
- MDMI 1.4/2.0 OUT
- M.2 E-Key SDIO slot
- USB 3.0 Port
- USB Type-C 5V Power

Signed-off-by: Tianling Shen <cnsztl@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>