ramips: add support for Lava LR-25G001

ramips: add support for Lava LR-25G001

The Lava LR-25G001 Wireless Router is based on the MT7620A SoC.

Specification:

- MediaTek MT7620A (580 Mhz)
- 64 MB of RAM
- 16 MB of FLASH
- 1x 802.11bgn radio
- 1x 802.11ac radio (MT7610EN)
- 5x 10/100/1000 Mbps AR8337 Switch (1 WAN AND 4 LAN)
- 2x external, detachable antennas
- 1x USB 2.0
- UART (J3) header on PCB (57600 8n1)
- 8x LED (3x GPIO-controlled), 2x button
- JBOOT bootloader

Known issues:
- Work only three Gigabit ports (3/5, 1 WAN and 2LAN)

Installation:
Apply factory image via http web-gui or JBOOT recovery page

How to revert to OEM firmware:
- push the reset button and turn on the power. Wait until LED start
  blinking (~10sec.)
- upload original factory image via JBOOT http (IP: 192.168.123.254)

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