mediatek: filogic: add support for Ubiquiti UniFi 6 Plus (U6+)

mediatek: filogic: add support for Ubiquiti UniFi 6 Plus (U6+)

Ubiquiti U6+ is a dual-band WiFi 6 PoE access point.
It is a drop-in upgrade of the U6 lite.

Specifications
---

- SoC: MediaTek MT7981A dual-core ARM Cortex-A53 1.3 GHz
- RAM: 256 MB DDR3-2133 RAM
- Flash: 16 MB SPI NOR and 4 GB eMMC
- LAN: 1x Gigabit Ethernet with 802.3af/at support
- WLAN: MediaTek MT7976C 2x2 MIMO dual-band WiFi 6
- LEDs: 1x blue and 1x white
- Buttons: 1x reset button

Installation
---

1. Power device using a PoE injector or switch
2. Connect via Ethernet to the device with static IP 192.168.1.2
3. SSH into the device with password: ubnt

        $ ssh ubnt@192.168.1.20

4. Unlock kernel partitions for writing

        $ echo 5edfacbf > /proc/ubnthal/.uf

5. Confirm correct partitions

        $ grep PARTNAME /sys/block/mmcblk0/mmcblk0p6/uevent
        PARTNAME=kernel0
        $ grep PARTNAME /sys/block/mmcblk0/mmcblk0p7/uevent
        PARTNAME=kernel1
        $ grep PARTNAME /sys/block/mmcblk0/mmcblk0p8/uevent
        PARTNAME=bs

6. Set and confirm bootloader environment

        $ fw_setenv boot_openwrt "fdt addr \$(fdtcontroladdr); fdt rm /signature; bootubnt"
        $ fw_setenv bootcmd_real "run boot_openwrt"
        $ fw_printenv

7. Copy sysupgrade image to /tmp/openwrt.bin via scp
8. Copy kernel and rootfs to mmcblk0p6 and mmcblk0p7, respectively

        $ tar xf /tmp/openwrt.bin sysupgrade-ubnt_unifi-6-plus/kernel -O | dd of=/dev/mmcblk0p6
        $ tar xf /tmp/openwrt.bin sysupgrade-ubnt_unifi-6-plus/root -O | dd of=/dev/mmcblk0p7

9. Ensure device boots from mmcblk0p6

        $ echo -ne "\x00\x00\x00\x00\x2b\xe8\x4d\xa3" > /dev/mmcblk0p8

10. Reboot the device

        $ reboot

Signed-off-by: Elbert Mai <code@elbertmai.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
(cherry picked from commit 75ee5546e9b7cfa5bbfd6f844ab8c5fffd5bb594)