ar71xx: add support for 8devices Lima board

Lima is a module for the (IoE) internet of everything applications,
based on Qualcomm/Atheros QCA4531.

Specification:

- 650/600/216 MHz (CPU/DDR/AHB)
- 64 MB of RAM (DDR2)
- 32 MB of FLASH
- 2T2R 2.4 GHz
- 2x 10/100 Mbps Ethernet
- USB 2.0 Host
- PCIe
- UART for serial console
- 14x GPIO

Flash instruction:
1. Download lede-ar71xx-generic-lima-squashfs-sysupgrade.bin
and rename it to 8dev_recovery.bin
2. Binary file copy to USB stick and plug into slot USB
3. Press S2 (reset) button
4. Press and hold the S1 button by 5 seconds
5. Wait ~40 seconds to complete recovery

Tested on:

- Lima development kit

Signed-off-by: Karol Dudek <karoiz@sli.pl>