ath79: add support for ALFA Network WiFi CampPro Nano Duo

ath79: add support for ALFA Network WiFi CampPro Nano Duo

ALFA Network WiFi CampPro Nano Duo is a dual-radio Wi-Fi signal extender
(router) in USB dongle form-factor (Type-A plug is used only for power),
based on combination of two radio chipsets: Qualcomm QCA9531 (main SOC)
and MediaTek MT7610U (connected over USB 2.0 interface).

Specifications:

- SOC:      QCA9531 v2 (650 MHz)
- DRAM:     DDR2 128 MiB (Nanya NT5TU64M16HG-AC)
- Flash:    16 MiB SPI NOR (Macronix MX25L12835F)
- Ethernet: 1x 10/100 Mbps Ethernet (QCA9531)
- Wi-Fi:    2x2:2 2.4   GHz Wi-Fi 4 (QCA9531)
            1x1:1 2.4/5 GHz Wi-Fi 5 (MT7610U)
- Antenna:  3x RP-SMA (female) antenna connectors
- LED:      1x orange (RJ45, power indicator)
            2x green  (status + RJ45 activity/link)
            1x blue   (Wi-Fi 2.4 GHz status)
- Button:   1x button (reset)
- UART:     1x 4-pin, 2.00 mm pitch header on PCB
- Other:    external h/w watchdog (EM6324QYSP5B, enabled by default)
            GPIO-controlled USB power for MT7610U

MAC addresses:

- LAN:                 00:c0:ca:xx:xx:6d (art 0x2, -1)
- 2.4 GHz (QCA9531):   00:c0:ca:xx:xx:6e (art 0x2, device's label)
- 2.4/5 GHz (MT7610U): 00:c0:ca:xx:xx:6f (from eeprom)

Flash instructions:

You can use sysupgrade image directly in vendor firmware which is based
on LEDE/OpenWrt. 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 RJ45 port, press the reset button, power up device,
   wait for first blink of status LED (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>