ramips: add support for Cudy WR1300 v2

ramips: add support for Cudy WR1300 v2

Specifications:
 - SoC: MediaTek MT7621AT
 - RAM: 128 MB (DDR3)
 - Flash: 16 MB (SPI NOR)
 - WiFi: MediaTek MT7603E, MediaTek MT7613BE
 - Switch: 1 WAN, 4 LAN (Gigabit)
 - Ports: 1 USB 3.0
 - 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.

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: Óscar García Amor <ogarcia@connectical.com>