ath79: add support for Qxwlan E600G v2 / E600GAC v2

E600G v2 based on Qualcomm/Atheros QCA9531

Specification:

 - 650/600/200 MHz (CPU/DDR/AHB)
 - 128/64 MB of RAM (DDR2)
 - 8/16 MB of FLASH (SPI NOR)
 - 2T2R 2.4 GHz
 - 2 x 10/100 Mbps Ethernet(RJ45)
 - 1 x MiniPCI-e
 - 1 x SIM (3G/4G)
 - 5 x LED , 1 x Button(SW2-Reset Buttun), 1 x power input
 - UART(J100) header on PCB(115200 8N1)

E600GAC v2 based on Qualcomm/Atheros QCA9531 + QCA9887

Specification:

 - 650/600/200 MHz (CPU/DDR/AHB)
 - 128/64 MB of RAM (DDR2)
 - 8/16 MB of FLASH (SPI NOR)
 - 2T2R 2.4 GHz
 - 1T1R 5 GHz
 - 2 x 10/100 Mbps Ethernet(RJ45)
 - 6 x LED (one three-color led), 2 x Button(SW2-Reset Buttun),1 x power input
 - UART (J100)header on PCB(115200 8N1)

Flash instruction:

1.Using tftp mode with UART connection and original OpenWrt image
 - Configure PC with static IP 192.168.1.10 and tftp server.
 - Rename "openwrt-ath79-generic-xxx-squashfs-sysupgrade.bin"
   to "firmware.bin" and place it in tftp server directory.
 - Connect PC with one of LAN ports, power up the router and press
   key "Enter" to access U-Boot CLI.
 - Use the following commands to update the device to OpenWrt:
   run lfw
 - After that the device will reboot and boot to OpenWrt.
 - Wait until all LEDs stops flashing and use the router.

2.Using httpd mode with Web UI connection and original OpenWrt image
 - Configure PC with static IP 192.168.1.xxx(2-255) and tftp server.
 - Connect PC with one of LAN ports,press the reset button, power up
   the router and keep button pressed for around 6-7 seconds, until
   leds flashing.
 - Open your browser and enter 192.168.1.1,You will see the upgrade
   interface, select "openwrt-ath79-generic-xxx-squashfs-
   sysupgrade.bin" and click the upgrade button.
 - After that the device will reboot and boot to OpenWrt.
 - Wait until all LEDs stops flashing and use the router.

Signed-off-by: 张鹏 <sd20@qxwlan.com>
[rearrange in generic.mk, fix one case in 04_led_migration, update
commit message]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>