ar71xx: add support for AR9331 based Hak5 devices

ar71xx: add support for AR9331 based Hak5 devices

This adds support for AR9331 based Hak5 penetration testing tools:

- WiFi Pineapple NANO
- LAN Turtle
- Packet Squirrel

WiFi Pineapple NANO specifications:

- SoC: Atheros AR9331 (400 MHz)
- RAM: 64 MB (DDR2)
- FLASH: 16 MB
- WiFi: 1T1R AR9331 (built-in), 1T1R AR9271 (built-in via USB bus)
- Ethernet: 1x FE over USB (ASIX AX88772A)
- Ports: 2x RP-SMA for antennas, 1x USB 2.0 (host), 1x micro SD
- Power: USB 5 V, 1.5 A
- Other: status LED, reset button

LAN Turtle specifications:

- SoC: Atheros AR9331 (400 MHz)
- RAM: 64 MB (DDR2)
- FLASH: 16 MB
- WiFi: none
- Ethernet: 1x FE (AR9331), 1x FE over USB (Realtek RTL8152B)
- Ports: 1x RJ45, version dependent: micro SD or 3G SIM slot
- Power: USB 5 V, 0.5 A
- Other: status LED, reset button (inside, on PCB)

Packet Squirrel specifications:

- SoC: Atheros AR9331 (400 MHz)
- RAM: 64 MB (DDR2)
- FLASH: 16 MB
- WiFi: none
- Ethernet: 2x FE (AR9331)
- Ports: 2x RJ45, 1x USB 2.0
- Power: USB 5 V, 0.12 A
- Other: status LED, reset button, 4-way switch

Flash instructions for all 3 devices:

Original firmware is based on OpenWrt.
Use sysupgrade via SSH to flash.

Signed-off-by: Sebastian Kinne <contact@sebkinne.com>
[squashed commits, combined and reworked mach files, aligned board
naming with general convention, fixed minor issues, tested on real
hardware, reworded commit subject and description]
Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>