mediatek: add support for Buffalo WSR-6000AX8 and AX8P

mediatek: add support for Buffalo WSR-6000AX8 and AX8P

This commit adds support for Buffalo WSR-6000AX8 and AX8P models.

Hardware
--------
SOC:       MediaTek MT7986B
RAM:       512MB
FLASH:     128MB SPI-NAND (Winbond)
WIFI 2.4G: (Embedded in SOC) b/g/n/ax, MIMO 4x4
WIFI 5G:   (Embedded in SOC) a/n/ac/ax, MIMO 4x4
ETHERNET:  2.5GbE MaxLinear GPY211C (eth1: WAN)
ETHERNET:  MediaTek MT7531AE 3xGbE (eth0: LAN1, LAN2, LAN3)
UART:      3.3V 115200 8N1

Serial(UART) Pin Layout
-----------------------

   +-------+-------+-------+-------+
J4 |  RX   |  TX   |  GND  |(3.3V) |
   +-------+-------+-------+-------+
           (Bottom Side)

MAC Address Table
-----------------
lan1-3:    board_data 0x4(text)
eth1/WAN:  board_data 0x4(text)
WIFI 2.4G: lan1 + 2
WIFI 5G:   lan1 + 9

Installation
------------

1. Set up a TFTP server with the IP address "192.168.11.2".

2. Rename the OpenWrt initramfs image to "linux.ubi-recovery" and place it
   in the TFTP server's root directory.
3. While holding down the AOSS button, power on the WSR-6000AX8 (or AX8P).

4. The device will automatically download the initramfs image
   from the TFTP server and boot into it.
5. Once booted, run "sysupgrade -n" using the OpenWrt sysupgrade image
   to complete the installation.

Recovery
--------

1. Decrypt the official firmware image using "buffalo-enc".

   example:
   $ buffalo-enc -d -i wsr_6000ax8_jp_100 -o wsr_6000ax8_jp_100.dec \
     -l -O 0xc8

2. Run "sysupgrade -F -n" with the decrypted image.

Signed-off-by: Shin Sato <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/13107
Signed-off-by: Hauke Mehrtens <[email protected]>