ath79: add support for COMFAST CF-E5/E7

ath79: add support for COMFAST CF-E5/E7

COMFAST CF-E5/E7 is a outdoor 4G LTE AP with PoE support, based on
Qualcomm/Atheros QCA9531.

Short specification:

    2x 10/100 Mbps Ethernet, with 24v PoE support
    64 MB of RAM (DDR2)
    16 MB of FLASH (SPI)
    2T2R 2.4 GHz, 802.11b/g/n
    built-in 1x 3 dBi antennas
    output power (max): 80 mW (19 dBm)
    Qucetel EC20 LTE MODULE(1x external detachable antenna)

Flash instruction:

Original firmware is based on OpenWrt.
Use sysupgrade image directly in vendor GUI.

Signed-off-by: Ding Tengfei <dtf@comfast.cn>
[commit subject fix]
Signed-off-by: Petr Štetiar <ynezz@true.cz>