ramips: add support for GL.iNet microuter-N300

ramips: add support for GL.iNet microuter-N300

The GL.iNet microuter-N300 (internally referred as MT300N-v4) is a
pocket-size travel router. It is essentially identical to the VIXMINI
(internally referred as MT300N-v3) but with double the RAM and
SPI-flash.

Additionally, set the label-mac for both the VIXMINI as well as the
microuter-N300.

Hardware
--------
SoC:   MediaTek MT7628NN
RAM:   128M DDR2
FLASH: 16M
LED:   Power - WLAN
BTN:   Reset
UART:  115200 8N1
       TX and RX are labled on the board as pads next to the SoC

Installation via web-interface
------------------------------
1. Visit the web-interface at 192.168.8.1
   Note: The ethernet port is by default WAN. So you need to connect to
   the router via WiFi

2. Navigate to the Update tab on the left side.

3. Select "Local Update"

4. Upload the OpenWrt sysupgrade image.
   Note: Make sure you select not to preserve the configuration.

Installation via U-Boot
-----------------------
1. Hold down the reset button while powering on the device.
   Wait for the LED to flash 5 times.

2. Assign yourself a static IPv4 in 192.168.1.0/24

3. Upload the OpenWrt sysupgrade image at 192.168.1.1.

Signed-off-by: David Bauer <mail@david-bauer.net>