ramips: Add support for Cudy WR1300 v3

ramips: Add support for Cudy WR1300 v3

Specifications:
 - SoC: MediaTek MT7621AT
 - RAM: 128 MB (DDR3)
 - Flash: 16 MB (SPI NOR)
 - WiFi: MediaTek MT7603E, MediaTek MT7613BE
 - Switch: 1 WAN, 4 LAN (Gigabit)
 - Buttons: Reset, WPS
 - LEDs: System, Wan, Lan 1-4, WiFi 2.4G, WiFi 5G, WPS
 - Power: DC 12V 1A tip positive

Download and flash the manufacturer's built OpenWRT image available at
http://www.cudytech.com/openwrt_software_download
Install the new OpenWRT image via luci (System -> Backup/Flash firmware)
Be sure to NOT keep settings. The force upgrade may need to be checked
due to differences in router naming conventions.

Cudy WR1300 v3 differs from v2 only in swapped WiFi chip PCIe slots. Common
nodes are extracted to .dtsi and new v2 and v3 dts are created.

Cudy WR1300 v2 dts now contains ieee80211-freq-limit and has
eeprom_factory_8000 length fixed.

The same manufacturer's built OpenWRT image is provided for both v2 and v3
devices as a step in installing, but for proper WiFi functionality,
a separate build is required.

Recovery:
 - Loads only signed manufacture firmware due to bootloader RSA verification
 - serve tftp-recovery image as /recovery.bin on 192.168.1.88/24
 - connect to any lan ethernet port
 - power on the device while holding the reset button
 - wait at least 8 seconds before releasing reset button for image to
   download
 - See http://www.cudytech.com/newsinfo/547425.html

Signed-off-by: Filip Milivojevic <zekica@gmail.com>