ramips: add support for DLINK DIR-510L

ramips: add support for DLINK DIR-510L

The DIR-510L Wireless Router are based on the MT7620A SoC.

Specification:

-MediaTek MT7620A (580 Mhz)
-128 MB of RAM
-16 MB of FLASH
-802.11bgn radio
-1x 10/100 Mbps Ethernet
-2x internal, non-detachable antennas
-UART (J3) header on PCB (57600 8n1)
-1x bi-color LED (GPIO-controlled), 2x button
-JBOOT bootloader

Known issues:
-Ethernet port is used as LAN
-No communication with charger IC. (uart bitbang needed)

Installation:
Apply factory image via d-link http web-gui.

How to revert to OEM firmware:
1.) Push the reset button and turn on the power. Wait until LED start blinking (~10sec.)
2.) Upload original factory image via JBOOT http (IP: 192.168.123.254)
3.) If http doesn't work, it can be done with curl command:
    curl -F FN=@XXXXX.bin http://192.168.123.254/upg
    where XXXXX.bin is name of firmware file.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
[fixed whitespace issue in 10-rt2x00-eeprom]
Signed-off-by: Petr Štetiar <ynezz@true.cz>