mediatek: add Comfast CF-E393AX support

mediatek: add Comfast CF-E393AX support

Comfast CF-E393AX is a dual-band Wi-Fi 6 POE ceiling mount access point.

Oem firmware is a custom openwrt 21.02 snapshot version.

We can gain access via ssh once we remove the root password.

Hardware specification:
  SoC: MediaTek MT7981A 2x A53
  Flash: 128 MB SPI-NAND
  RAM: 256MB DDR3
  Ethernet: 1x 10/100/1000 Mbps built-in PHY (WAN)
            1x 10/100/1000/2500 Mbps MaxLinear GPY211C (LAN)
  Switch: MediaTek MT7531AE
  WiFi: MediaTek MT7976D
  LEDS: 1x (Red, Blue and Green)
  Button: Reset
  UART: 3.3v, 115200n8
  --------------------------
  | Layout |
  | ----------------- |
  | 4 | VCC GND TX RX | <= |
  | ----------------- |
  --------------------------

Gain SSH access:
1. Login into web interface (http://apipaddress/computer/login.html),
   and download the
   configuration(http://apipaddress/computer/config.html).

2. Rename downloaded backup config - 'backup.file to backup.tar.gz',
   Enter 'fakeroot' command then decompress the configuration:
   tar -zxf backup.tar.gz

3. Edit 'etc/shadow', update (remove) root password:
   With password =
   'root:$1$xf7D0Hfg$5gkjmvgQe4qJbe1fi/VLy1:19362:0:99999:7:::'
   'root:$1$xf7D0Hfg$5gkjmvgQe4qJbe1fi/VLy1:19362:0:99999:7:::'
   to
   Without password =
   'root::0:99999:7:::'
   'root::0:99999:7:::'

4. Repack 'etc' directory back to a new backup file:
   tar -zcf backup-ssh.tar.gz etc/
5. Rename new config tar.gz file to 'backup-ssh.file'
   Exit fakeroot - 'exit'

6. Upload new configuration via web interface, now you
   can SSH with the following:

   'ssh -vv -o HostKeyAlgorithms=+ssh-rsa \
   -o PubkeyAcceptedAlgorithms=+ssh-rsa root@192.168.10.1'.

   Backup the mtd partitions
   - https://openwrt.org/docs/guide-user/installation/generic.backup

7. Copy openwrt factory firmware to the tmp folder to install via ssh:

   'scp -o HostKeyAlgorithms=+ssh-rsa \
   -o PubkeyAcceptedAlgorithms=+ssh-rsa \
   *-mediatek-filogic-comfast_cf-e393ax-squashfs-factory.bin \
   root@192.168.10.1:/tmp/'

   'sysupgrade -n -F \
   /tmp/*--mediatek-filogic-comfast_cf-e393ax-squashfs-factory.bin'

8. Once led has stopped flashing - Connect via ssh with the
   default openwrt ip address - 'ssh root@192.168.1.1'

9. SSH copy the openwrt sysupgrade firmware and upgrade
   as per the default instructions.

Signed-off-by: David Bentham <db260179@gmail.com>