ath79: add support for WD My Net N600

ath79: add support for WD My Net N600

SoC: AR9344
RAM: 128MB
Flash: 16MiB SPI NOR
5GHz WiFi: AR9382 PCIe 2x2:2 802.11n
2.4GHz WiFi: AR9344 (SoC) AHB 2x2:2 802.11n

5x Fast ethernet via SoC switch (green LEDs)
1x USB 2.0
4x front LEDs from SoC GPIO
1x front WPS button from SoC GPIO
1x bottom reset button from SoC GPIO

UART header JP1, 115200 no parity 1 stop
TX
GND
VCC
(N/P)
RX

Flash factory image via "emergency room" recovery:
- Configure your computer with a static IP 192.168.1.123/24
- Connect to LAN port on the N600 switch
- Hold reset putton
- Power on, holding reset until the power LED blinks slowly
- Visit http://192.168.1.1/ and upload OpenWrt factory image
- Wait at least 5 minutes for flashing, reboot and key generation
- Visit http://192.168.1.1/ (OpenWrt LuCI) and upload OpenWrt sysupgrade image

Signed-off-by: Ryan Mounce <ryan@mounce.com.au>
[dt leds preparations]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>