ramips: add support for Motorola MWR03

ramips: add support for Motorola MWR03

Specifications:
* SOC: MT7628AN + MT7612E
* ROM: 8 MiB Flash
* RAM: 64 MiB DDR2
* WAN: 10/100M *1
* LAN: 10/100M *3
* Button: Reset *1
* LEDs: orange *1, white *1
* Antennas: 2.4 GHz *2 + 5 GHz *2
* TTL Baudrate: 57600
* TFTP Upgrade: IP: 192.168.51.1, Server: 192.168.51.100

MAC addresses as verified by OEM firmware:

use   address   source
2g    *:d8      factory 0x0004 (label)
5g    *:d9      factory 0x8004
LAN   *:d7      factory $label -1
WAN   *:da      factory $label +2

Installation (TFTP + U-Boot):
 * Connect device with a TTL cable and open a serial session by
   PuTTY.
 * Press "2" when booting to select "Load system code then write
   to Flash via TFTP".
 * Configure the IP of local host server.
 * Upload firmware by tftpd64, it will boot when write instruction
   is executed.

Signed-off-by: Shiji Yang <yangshiji66@qq.com>
[fix DTS line endings, fix label MAC address, adjust status LED
 names, convert mtd-mac-address-increment to mac-address-increment]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>