ath79: support for TP-Link EAP225-Outdoor v1

ath79: support for TP-Link EAP225-Outdoor v1

TP-Link EAP225-Outdoor v1 is an AC1200 (802.11ac Wave-2) pole or wall
mount access point. Debricking requires access to the serial port, which
is non-trivial.

Device specifications:
* SoC: QCA9563 @ 775MHz
* Memory: 128MiB DDR2
* Flash: 16MiB SPI-NOR
* Wireless 2.4GHz (SoC): b/g/n 2x2
* Wireless 5GHz (QCA9886): a/n/ac 2x2 MU-MIMO
* Ethernet (AR8033): 1× 1GbE, PoE

Flashing instructions:
* ssh into target device with recent (>= v1.6.0) firmware
* run `cliclientd stopcs` on target device
* upload factory image via web interface

Debricking:
To recover the device, you need access to the serial port. This requires
fine soldering to test points, or the use of probe pins.
* Open the case and solder wires to the test points: RXD, TXD and TPGND4
  * Use a 3.3V UART, 115200 baud, 8n1
* Interrupt bootloader by holding ctrl+B during boot
* upload initramfs via built-in tftp client and perform sysupgrade
    setenv ipaddr 192.168.1.1 # default, change as required
    setenv serverip 192.168.1.10 # default, change as required
    tftp 0x80800000 initramfs.bin
    bootelf $fileaddr

MAC addresses:
MAC address (as on device label) is stored in device info partition at
an offset of 8 bytes. ath9k device has same address as ethernet, ath10k
uses address incremented by 1.
From stock ifconfig:

    ath0      Link encap:Ethernet  HWaddr D8:...:2E
    ath10     Link encap:Ethernet  HWaddr D8:...:2F
    br0       Link encap:Ethernet  HWaddr D8:...:2E
    eth0      Link encap:Ethernet  HWaddr D8:...:2E

Tested by forum user PolynomialDivision on firmware v1.7.0.
UART access tested by forum user arinc9.

Signed-off-by: Sander Vanheule <sander@svanheule.net>