ar71xx: add support for COMFAST CF-E385AC

ar71xx: add support for COMFAST CF-E385AC

COMFAST CF-E385AC is an AC2200 ceiling mount AP with PoE support, based
on Qualcomm/Atheros QCA9558 + QCA9984 + QCA8337N.

Specification:

- 720/600/200 MHz (CPU/DDR/AHB)
- 256 MB of RAM (DDR2)
- 16 MB of FLASH (SPI NOR)
- 2x 10/100/1000 Mbps Ethernet, with PoE support
- 3T3R 2.4 GHz (QCA9558), with external LNA and PA (SE2576L)
- 4T4R 5 GHz (QCA9984), with external FEM (SKY85728-11)
- 7x internal antennas
- 1x RGB LED (driven by GPIO)
- 1x button (reset)
- UART, LEDs/GPIO and USB headers on PCB
- external watchdog (Pericon Technology PT7A7514)

Flash instruction:

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

Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>