ar71xx: add support for ALFA Network N5Q

ar71xx: add support for ALFA Network N5Q

ALFA Network N5Q is a successor of previous model, the N5 (outdoor
CPE/AP, based on Atheros AR7240 + AR9280). New version is based on
Atheros AR9344.

Specification:

- 550/400/200 MHz (CPU/DDR/AHB)
- 64 MB of RAM (DDR2)
- 16 MB of FLASH (SPI NOR)
- 2x 10/100 Mbps Ethernet, with passive PoE support (24 V)
- 2T2R 5 GHz (AR9344), with ext. PA (RFPA5542) and LNA, up to 27 dBm
- 8x LED (7 are driven by GPIO)
- 1x button (reset)
- external h/w watchdog (EM6324QYSP5B, disabled and not used)
- header for optional 802.3at/af PoE module
- DC jack for main power input (optional, not installed by default)
- UART header on PCB

Flash instruction:

You can use sysupgrade image directly in vendor firmare which is based
on OpenWrt/LEDE. Alternatively, you can use web recovery mode in U-Boot:

1. Configure PC with static IP 192.168.1.2/24.
2. Connect PC with one of RJ45 ports, press the reset button, power up
   device, wait for first blink of all LEDs (indicates network setup),
   then keep button for 3 following blinks and release it.
3. Open 192.168.1.1 address in your browser and upload sysupgrade image.

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