ath79: add support for ASUS RP-AC66

ath79: add support for ASUS RP-AC66

Asus RP-AC66 Repeater

Hardware specifications:
Board: AP152
SoC: QCA9563
DRAM: 64MB DDR2
Flash: 25l128 16MB SPI-NOR
LAN/WAN: 1x1000M QCA8033
WiFi 5GHz: QCA9880
Clocks: CPU:775.000MHz, DDR:650.000MHz, AHB:258.333MHz, Ref:25.000MHz

MAC addresses as verified by OEM firmware:
use            address   source
Lan/Wan   *:24         art 0x1002 (label)
2G             *:24         art 0x1002
5G             *:26         art 0x5006

Installation:

Asus windows recovery tool:
 - install the Asus firmware restoration utility
 - unplug the router, hold the reset button while powering it on
 - release when the power LED flashes slowly
 - specify a static IP on your computer:
     IP address: 192.168.1.75
     Subnet mask 255.255.255.0
 - Start the Asus firmware restoration utility, specify the factory image
    and press upload
 - Do not power off the device after OpenWrt has booted until the LED flashing.

TFTP Recovery method:
 - set computer to a static ip, 192.168.1.75
 - connect computer to the LAN 1 port of the router
 - hold the reset button while powering on the router for a few seconds
 - send firmware image using a tftp client; i.e from linux:
 $ tftp
 tftp> binary
 tftp> connect 192.168.1.1
 tftp> put factory.bin
 tftp> quit

Signed-off-by: Tamas Balogh <tamasbalogh@hotmail.com>