ramips: Add support for D-Link DIR-3060 A1

ramips: Add support for D-Link DIR-3060 A1

Hardware specification:
SoC: MediaTek MT7621AT
Flash: Winbond W29N01HVSINA 128MB
RAM: Micron MT41K128M16JT-125 256MB
Ethernet: 4x 10/100/1000 Mbps
WiFi1: MT7615DN 2.4GHz N 2x2:2
WiFi2: MT7615DN 5GHz AC 2x2:2
WiFi3: MT7615N 5GHz AC 4x4:4
Button: WPS, Reset

Flash instructions:
OpenWrt can be installed via D-Link Recovery GUI:

    Push and hold reset button (on the bottom of the device) until power led starts flashing (about 10 secs or so) while plugging in the power cable.
    Give it ~30 seconds, to boot the recovery mode GUI
    Connect your client computer to LAN1 of the device
    Set your client IP address manually to 192.168.0.2 / 255.255.255.0.
    Call the recovery page for the device at http://192.168.0.1/
    Use the provided emergency web GUI to upload and flash a new firmware to the device

Signed-off-by: Ivaylo Ivanov <iivailo@mail.bg>