ramips: add support for Cudy WR1300

ramips: add support for Cudy WR1300

Specifications:
 - SoC: MediaTek MT7621AT
 - RAM: 128 MB (DDR3)
 - Flash: 16 MB (SPI NOR)
 - WiFi: MediaTek MT7603E, MediaTek MT7612E
 - Switch: 1 WAN, 4 LAN (Gigabit)
 - Ports: 1 USB 3.0
 - Buttons: Reset, WPS
 - LEDs: Power, System, Wan, Lan 1-4, WiFi 2.4G, WiFi 5G, WPS, USB
 - Power: DC 12V 1A tip positive

UART Serial:
  115200 baud
  Located on unpopulated 4 pin header near J4:

  J4
  [o] Rx
  [o] Tx
  [o] GND
  [ ] Vcc - Do not connect

Installation:

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

MAC addresses as verified by OEM firmware:

use   address   source
LAN   *:f0      label
WAN   *:f1      label + 1
2g    *:f0      label
5g    *:f2      label + 2

The label MAC address is found in bdinfo 0xde00.

Signed-off-by: Andrew Pikler <andrew.pikler@gmail.com>