ramips: add support for D-Link DRA-1360

ramips: add support for D-Link DRA-1360

The DRA-1360 rev A is a wall-plug AC1300 repeater.
Hardware is identical (same FCC ID, black case instead of white)
to D-Link DAP-1620 rev B, which is already supported, but a
different model name, revision, and hardware ID are needed.
Thus, the bulk of the DAP-1620 device tree is extracted to a
common dtsi included by the two models' device trees.

Repeating specs and installation instructions from e4c7703:
(note that the RAM size mentioned there was incorrect, oops)

Specs:
- SoC: MT7621AT (880MHz dual-core MIPS1004Kc)
- Memory: 128 MiB RAM, 16 MiB NOR SPI
- WiFi: MT7615DN 2x2 802.11n + 2x2 802.11ac (DBDC)
- Ethernet: 1 RJ45 port 10/100/1000
- Power/status LED: red+green
- LED RSSI bargraph: 2x green, 1x red+green

Installation:
- Keep reset button pressed during plug-in
- Web Recovery Updater is at 192.168.0.50
  (pings are ignored, it listens only for http)
- Upload factory.bin, confirm flashing
  (seems to work best with Chromium-based browsers)

Revert to OEM firmware:
- tail -c+117 DRA1360A1_FW112B03.bin | \
  openssl aes-256-cbc -d -md md5 -out decrypted.bin \
  -k c471706398cb147c6619f8a04a18d53e9c17ede8
- flash decrypted.bin via D-Link Web Recovery

Signed-off-by: Rani Hod <rani.hod@gmail.com>