rockchip: add support for Radxa ROCK 3B

rockchip: add support for Radxa ROCK 3B

Radxa ROCK 3B is a Pico-ITX form factor SBC[1] using the Rockchip
RK3568(J).

Hardware
--------
- Rockchip RK3568(J) SoC
- Quad A55 CPU
- Mali-G52 GPU
- 1 TOPS @ INT8 NPU
- 2GB/4GB/8GB LPDDR4 RAM
- eMMC connector
- Micro SD Card slot
- NVMe SSD through the M.2 M Key (2-lane PCIe 3.0)
- SPI Flash for bootloader
- 2x Gigabit ethernet port (one supports PoE with add-on PoE HAT)
- 1x M.2 E Key socket with SDIO, UART and USB interfaces
- 1x M.2 B Key socket with PCIe, SATA, and USB interfaces
- 1x SIM card socket
- 1x USB 3.0 Type-A HOST port
- 1x USB 3.0 Type-A OTG port
- 2x USB 2.0 Type-A HOST ports
- 40 Pin GPIO header

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

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>