ramips: cf-ew72-v2: Add support for COMFAST CF-EW72 V2

ramips: cf-ew72-v2: Add support for COMFAST CF-EW72 V2

Add support for COMFAST CF-EW72 V2

Hardware:
-   SoC: Mediatek MT7621 (MT7621DAT or MT7621AT)
-   Flash: 16 MiB NOR
-   RAM: 128 MiB
-   Ethernet: Built-in, 2 x 1GbE
-   Power: only 802.3af PD on any port, injector supplied in the box
-   PoE passthrough: No
-   Wifi 2.4GHz: Mediatek MT7603BE 802.11b/g/b
-   Wifi 5GHz: Mediatek MT7613BEN 802.11ac/n/a
-   LEDs: 8x (only 1 is both visible and controllable, see below)
-   Buttons: 1x (RESET)

Installing OpenWrt:
Flashing is done using Mediatek U-Boot System Recovery Mode
-   make wired connection with 2 cables like this:
-     -   PC (LAN) <-> PoE Injector (LAN)
-     -   PoE Injector (POE) <-> CF-EW72 V2 (LAN). Leave unconnected to CF-EW72 V2 yet.
-   configure 192.168.1.(2-254)/24 static ip address on your PC LAN
-   press and keep pressed RESET button on device
-   power the device by plugging PoE Injector (POE) <-> CF-EW72 V2 (LAN) cable
-   wait for about 10 seconds until wifi led stops blinking and release RESET button
-   navigate from your PC to http://192.168.1.1 and upload OpenWrt *-factory.bin firmware file
-   proceed until router starts blinking with wifi led again (flashing) and stops (rebooting to OpenWrt)

MAC addresses as verified by OEM firmware:
  vendor OpenWrt  address
  LAN    lan\eth0 label
  WAN    wan     label + 1
  2g     phy0    label + 2
  5g     phy1    label + 3

  The label MAC address was found in 0xe000.

LEDs detailed:
  The only both visible and controllable indicator is blue:wlan LED.
  It is not bound by default to indicate activity of any wireless interfaces.

  Place (WAN->ANT) | Num | GPIO | LED name (LuCI)   | Note
  -----------------|-----|-----------------------------------------------------------------------------------------
             power | 1   |      |                   | POWER LED. Not controlled with GPIO.
      hidden_led_2 | 2   | 13   | blue:hidden_led_2 | This LED does not have proper hole in shell.
               wan | 3   |      |                   | WAN LED. Not controlled with GPIO.
      hidden_led_4 | 4   | 16   | blue:hidden_led_4 | This LED does not have proper hole in shell.
               lan | 5   |      |                   | LAN LED. Not controlled with GPIO.
      noconn_led_6 | 6   |      |                   | Not controlled with GPIO, possibly not connected
              wlan | 7   | 15   | blue:wlan         | WLAN LED. Wireless indicator.
      noconn_led_8 | 8   |      |                   | Not controlled with GPIO, possibly not connected

  mt76-phy0 and mt76-phy1 leds also exist in OpenWrt, but do not exist on board.

Signed-off-by: Alexey D. Filimonov <alexey@filimonic.net>