rockchip: add Lunzn FastRhino R66S support

rockchip: add Lunzn FastRhino R66S support

Hardware
--------
RockChip RK3568 ARM64 (4 cores)
1/2GB LPDDR4 RAM
2x 2500 Base-T (PCIe, r8125b)
1 LED (Power)
1 Button (Reset)
Micro-SD Slot
2x USB 3.0 Port
12V DC Jack

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

Tested-by: Francisco G Luna <frangonlun@gmail.com>
Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>
Link: https://github.com/openwrt/openwrt/pull/19990
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>