ar71xx: Add support for D-Link DAP-1330 a1

ar71xx: Add support for D-Link DAP-1330 a1

D-Link DAP-1330 rev. A1 is a wall-plug N300 Wi-Fi range extender,
based on Qualcomm/Atheros QCA9533 v2.

Short specification:

- 650/393/216 MHz (CPU/DDR/AHB)
- 1x 10/100 Mbps Ethernet
- 64 MB of RAM (DDR1)
- 8 MB of FLASH
- 2T2R 2.4 GHz
- 2x external antennas
- 6x LED (2 are bi-color), 2x button
- 4 pin on pcb (looking from eth port and from left to right tx,rx,gnd,vcc)

Flash instruction: use "factory" image directly in vendor GUI.

This device has a recovery system that assign the ip addr of env
variable "serverip" via dhcp to a pc, and the "ipaddr" value to itself.
The recovery it's triggered by a not bootable firmware,
or pressing the reset button during the bootloader startup (first 30 seconds).
The recovery uses a http page to restore the firmware, and it's checking
the firmware image header, so use the "factory" image to
restore or the original firmware.

You can access vendor firmware over serial using:
- login: root
- password: linuxrocks

Image was tested only in EU version of the device, but should work
also with the same device version sold in other countries.

Signed-off-by: Nicolò Veronese <nicveronese@gmail.com>