ath79: Add support for Ubiquiti Nanostation AC

ath79: Add support for Ubiquiti Nanostation AC

5 GHz AC wireless outdoor PoE CPE with internal 2.4 GHz management radio

CPU:    Atheros AR9342 SoC
RAM:    64 MB DDR2
Flash:  16 MB NOR SPI
Switch: QCA8334
Ports:  2 GbE ports (1x PoE in, 1x PoE passthrough)
WLAN:   5 GHz QCA899X (PCI) and 2.4 GHZ AR9342

Successor to the old NanoStation M5 with AC wireless.

The integrated QCA899X is a Ubiquiti branded part with modified vendor and
product id (0777:11ac9).

Serial

Serial settings: 115200, 8N1

* = plated through hole
0 = nylon screw

      [Top of device]
+--------------------------+
|    [label]               |
|  0                       |
|                    0     |
|         [ubnt]           |
|         [logo]  3V3  *   |
|                  TX  *   |
|                  RX  *   |
|                 GND  *   |
|                          |
|                      *   |
|                      *   |
|                      *   |
|                      *   |
|    0                     |
|                 0        |
|                          |
|                          |

Installation

1. Connect to serial header on device
2. Power on device and enter uboot console
3. Set up tftp server serving an openwrt initramfs build
4. Load initramfs build using the command tftpboot in the uboot cli
5. Boot the loaded image using the command bootm
6. Copy squashfs openwrt sysupgrade build to the booted device
7. Use mtd to write sysupgrade to partition "firmware"
8. Reboot and enjoy

Signed-off-by: Tobias Schramm <tobleminer@gmail.com>