ramips: add support for TRENDnet TEW-810DR

ramips: add support for TRENDnet TEW-810DR

Specifications:

* MediaTek MT7620A (580 Mhz)
* 8 MB of FLASH
* 64 MB of RAM
* 2.4Ghz and 5.0Ghz radios
* 5x 10/100 Mbps Ethernet (1 WAN and 4 LAN)
* UART header on PCB (57600 8n1)
* Green/Orange Power LEDs illuminating a Power-Button Lens
* Green/Orange Internet LEDs GPIO controlled illuminating a Globe/Internet Lens
* 3x button - wps, power and reset
* U-boot bootloader

Installation:

The sysupgrade.bin image is reported to be OEM web flashed with an ncc_att_hwid
appended.  ncc_att_hwid is a 32bit binary in the GPL Source download for either
the TEW-810DR or DIR-810L and is located at
source/user/wolf/cameo/ncc/hostTools.

The invocation is: ncc_att_hwid -f tew-810dr-squashfs-factory.bin -a -m "TEW-810DR" -H "1.0R" -r "WW" -c "1.0"

This may need to be altered if your hardware version is "1.1R".

The image can also be directly flashed via serial tftp:
1.  Load *.sysupgrade.bin to your tftp server directory and rename for
    convenience.
2.  Set a static ip 192.168.10.100.
3.  NIC cable to a lan port.
4.  Serial connection parameters 57600,8N1
5.  Power on the TEW-810 and press 4 for a u-boot command line prompt.
6.  Verify IP's with U-Boot command "printenv".
7.  Adjust tftp settings if needed per the tftp documentation
8.  Boot the tftp image to test the build.
9.  If the image loads, reset your server ip to 192.168.1.10 and restart network.
10. Log in to Luci, 192.168.1.1, and flash the *sysupgrade.bin image.

Notes:

The only valid MAC address is found in 0x28 of the factory partition.
Other typical offsets/caldata only contain example data: 00:11:22:00:0f:xx

Signed-off-by: J. Scott Heppler <shep971@centurylink.net>
[remove "link rx tx" in 01_leds, format and extend commit message,
fix DTS led node names]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>