ipq40xx: Add support for D-Link DAP-2610

ipq40xx: Add support for D-Link DAP-2610

Specifications
==============
- SOC: IPQ4018
- RAM: DDR3 256MB
- Flash: SPI NOR 16MB
- WiFi:
    - 2.4GHz: IPQ4018, 2x2, front end SKY85303-11
    - 5GHz: IPQ4018, 2x2, front end SKY85717-21
- Ethernet: 1x 10/100/1000Mbps, POE 802.3af
- PHY: QCA8072
- UART: GND, blocked, 3.3V, RX, TX / 115200 8N1
- LED: 1x red / green
- Button: 1x reset / factory default
- U-Boot bootloader with tftp and "emergency web server" accessible
  using serial port.

Installation
============
Flash factory image from D-Link web UI. Constraints in the D-Link web UI
makes the factory image unnecessarily large. Flash again using
sysupgrade from inside OpenWrt to reclaim some flash space.

Return to stock D-Link firmware
===============================
Partition layout is preserved, and it is possible to return to the stock
firmware simply by downloading it from D-Link and writing it to the
firmware partition.

    # mtd -r write dap2610-firmware.bin firmware

Quirks
======
To be flashable from the D-Link http server, the firmware must be larger
then 6MB, and the size in the firmware header must match the actual file
size. Also, the boot loader verifies the checksum of the firmware before
each boot, thus the jffs2 must be after the checksum covered part. This
is solved in the factory image by having the rootfs at the very end of
the image (without pad-rootfs).

The sysupgrade image which does not have to be flashable from the D-Link
web UI may be smaller, and the checksum in the firmware header only
covers the kernel part of the image.

Signed-off-by: Fredrik Olofsson <fredrik.olofsson@anyfinetworks.com>
[added WRGG Variables to DEVICE_VARS, squashed spi pinconf/mux,
added emd1's gmac0 config,fix dtc warnings]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>