ath79: add support for ALFA Network N5Q

ath79: 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.

Support for this device was first introduced in 4b0eebe9df (ar71xx
target) but users are advised to migrate from ar71xx target without
preserving settings as ath79 support includes some changes in network
and LED default configuration. They were aligned with vendor firmware
and recently added N2Q model (both Ethernet ports as LAN, labelled as
LAN1 and LAN2).

Specifications:

- Atheros AR9344
- 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 Wi-Fi, with ext. PA (RFPA5542) and LNA, up to 27 dBm
- 2x IPEX/U.FL or MMCX antenna connectors (for PCBA version)
- 8x LED (7 are driven by GPIO)
- 1x button (reset)
- external h/w watchdog (EM6324QYSP5B, enabled by default)
- header for optional 802.3at/af PoE module
- DC jack for main power input (optional, not installed by default)
- UART (4-pin, 2.54 mm pitch) header on PCB
- LEDs (2x 5-pin, 2.54 mm pitch) header on PCB

Flash instruction:

You can use sysupgrade image directly in vendor firmware 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>