rockchip: add support for Radxa ROCK 3C

rockchip: add support for Radxa ROCK 3C

Radxa ROCK 3C is a high-performance, low-cost SBC[1] using the
Rockchip RK3566.

Hardware
--------
- Rockchip RK3566 SoC
- Quad A55 CPU
- Mali-G52-2EE GPU
- 1 TOPS @ INT8 NPU
- 1GB/2GB/4GB LPDDR4 RAM
- eMMC connector
- Micro SD Card slot
- NVMe SSD through the M.2 M Key connector(2230) or M.2 Extension
  board(2232/2260/2280)
- SATA through the Radxa Penta SATA HAT
- 1x Gigabit ethernet port(supports PoE with add-on PoE HAT)
- WiFi6/BT5.4 (not supported yet on OpenWrt)
- 1x USB 3.0 Type-A HOST port
- 2x USB 2.0 Type-A HOST ports
- 1x USB 2.0 Type-A OTG port
- 40 Pin GPIO header

[1] https://radxa.com/products/rock3/3c

Installation
------------
Uncompress the OpenWrt sysupgrade and write it to a micro SD card or
internal eMMC using dd.

Signed-off-by: FUKAUMI Naoki <naoki@radxa.com>
Link: https://github.com/openwrt/openwrt/pull/16185
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>