ath79: add support for TP-Link TL-WA1201 v2

This device is a wireless access point working on the 2.4 GHz and 5 GHz
band, based on Qualcomm/Atheros QCA9563 + QCA9886.

Specification
- 775 MHz CPU
- 128 MB of RAM (DDR2)
- 16 MB of FLASH (SPI NOR)
- QCA9563: 2.4 GHz 3x3
- QCA9886: 5 GHz
- AR8033: 1x 1 Gbs Ethernet
- 4x LED, WPS factory reset and power button
- bare UART on PCB (accessible through testpoints)

Methods for Flashing:
- Apply factory image in OEM firmware web-gui. Wait a minute after the
  progress bar completes and restart the device.
- Sysupgrade on top of existing OpenWRT image
- Solder wires onto UART testpoints and attach a terminal.
  Boot the device and press enter to enter u-boot's menu. Then issue the
  following commands
  1. setenv serverip your-server-ip
     setenv ipaddr your-device-ip
  2. tftp 0x80060000 openwrt-squashfs.bin (Rembember output of size in
    hex, henceforth "sizeinhex")
  3. erase 0x9f030000 +"sizeinhex"
  4. cp.b 0x80060000 0x9f030000 0x"sizeinhex"
  5. reboot

Recover:
- U-boot serial console

Signed-off-by: Robert Balas <balasr@iis.ee.ethz.ch>
[convert to nvmem]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>