filogic: add support for Netgear WAX220

filogic: add support for Netgear WAX220

Hardware
--------
SOC:   MediaTek MT7986
RAM:   1024MB DDR3
FLASH: 128MB SPI-NAND (Winbond)
WIFI:  Mediatek MT7986 DBDC 802.11ax 2.4/5 GHz
ETH:   Realtek RTL8221B-VB-CG 2.5 N-Base-T PHY with PoE
UART:  3V3 115200 8N1 (Pinout silkscreened / Do not connect VCC)

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

1. Download the OpenWrt initramfs image. Copy the image to a TFTP server
2. Connect the TFTP server to the WAX220. Conect to the serial console,
   interrupt the autoboot process by pressing '0' when prompted.
3. Download & Boot the OpenWrt initramfs image.

   $ setenv ipaddr 192.168.2.1
   $ setenv serverip 192.168.2.2
   $ tftpboot openwrt.bin
   $ bootm

4. Wait for OpenWrt to boot. Transfer the sysupgrade image to the device
   using scp and install using sysupgrade.

   $ sysupgrade -n <path-to-sysupgrade.bin>

Signed-off-by: Flole Systems <flole@flole.de>
Signed-off-by: Stefan Agner <stefan@agner.ch>
(cherry picked from commit 984786a2f7ec622c99e8c9cdada65d0ea0cf4e0b)