ath79: add support for COMFAST CF-E375AC

ath79: add support for COMFAST CF-E375AC

COMFAST CF-E375AC is a ceiling mount AP with PoE support,
based on Qualcomm/Atheros QCA9563 + QCA9886 + QCA8337.

Short specification:

    2x 10/100/1000 Mbps Ethernet, with PoE support
    128MB of RAM (DDR2)
    16 MB of FLASH
    3T3R 2.4 GHz, 802.11b/g/n
    2T2R 5 GHz, 802.11ac/n/a, wave 2
    built-in 5x 3 dBi antennas
    output power (max): 500 mW (27 dBm)
    1x RGB LED, 1x button
    built-in watchdog chipset

Flash instruction:
1) Original firmware is based on OpenWrt.
Use sysupgrade image directly in vendor GUI.

2) TFTP
2.1) Set a tftp server on your machine with a fixed IP address of
     192.168.1.10. A place the sysupgrade as firmware_auto.bin.
2.2) boot the device with an ethernet connection on fixed ip route
2.3) wait a few seconds and try to login via ssh

3) TFTP trough Bootloader
3.1) open the device case and get a uart connection working
3.2) stop the autoboot process and test connection with serverip
3.3) name the sysupgrade image firmware.bin and run firmware_upg

MAC addresses:
Though the OEM firmware has four adresses in the usual locations,
it appears that the assigned addresses are just incremented in a
different way:

interface    address    location
LAN:          *:DC      0x0
WAN           *:DD      0x1002
WLAN 2.4g     *:E6      n/a (0x0 + 10)
WLAN 5g       *:DE      0x6
unused        *:DF      0x5006

The MAC address pointed at the label is the one assign to the LAN
interface.

Signed-off-by: Joao Henrique Albuquerque <joaohccalbu@gmail.com>
[add label-mac-device, remove redundant uart status, fix whitespace
issues, fix commit message wrapping, remove x bit on DTS file]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>