ramips: add support for D-Link DWR-116-A1/2

ramips: add support for D-Link DWR-116-A1/2

The DWR-116-A1/2 Wireless Router is based on the MT7620N SoC.

Specification:

  MediaTek MT7620N (580 Mhz)
  32 MB of RAM
  8 MB of FLASH
  802.11bgn radio
  5x 10/100 Mbps Ethernet (1 WAN and 4 LAN)
  2x external, non-detachable antennas
  UART (J1 in A1, JP1 in A2) header on PCB (57600 8n1)
  6x LED (GPIO-controlled), 2x button
  JBOOT bootloader

Known issues:
WAN LED is drived by uartl tx pin. I decide to use this pin as
uartlite tx pin.

Installation:
Apply factory image via http web-gui.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>