ath79: add support for Comfast WR650AC v1/v2

ath79: add support for Comfast WR650AC v1/v2

This is a dual band 11a/11n router with 1x wan and 4x gig lan ports.

There are two versions of this router which can be identified through
the factory web interface, v1 has 128mb ram and a uboot size of 128k,
v2 has 256mb ram and a uboot size of 256k, the remaining hardware and
PCB markings are the same.

Short specification:

    SoC: Qualcomm Atheros QCA9558 - 720 MHz
    Switch: Atheros AR8327
    Second radio : Qualcomm Atheros QCA9880 802.11ac
    4 LAN/1 WAN 1000Mps Ethernet
    256 MB of RAM (DDR2)
    16 MB of FLASH
    3x2.4 GHz, 3x5GHz antennas

Steps to install :

Option A : Use vendor UI

Option B (if A is not working) :
(a) Download 'backup' from vendor UI and rename it backup.tar.gz
(b) Open the archive, and update the root password in /etc/shadow by
    '$1$9wX3HGfB$X5Sb3kqzzBLdKRUR2kfFd0'
(c) 'Restore' from the archive using the vendor UI. Root password is now
    'aaa'
(d) Scp the firwmware to the device:
    $ scp <openwrt-sysupgrade>.bin root@192.168.1.1:/
(d) ssh to the device and flash the firmware:
    $ cd /
    $ mtd -e firmware -r write <openwrt-sysupgrade>.bin firmware

Signed-off-by: Gareth Parker <gareth41@orcon.net.nz>
Signed-off-by: Ding Tengfei <dtf@comfast.cn>
Signed-off-by: Joan Moreau <jom@grosjo.net>
[reformatted commit message]
Signed-off-by: David Bauer <mail@david-bauer.net>