ath79: add support for Aruba AP-115

ath79: add support for Aruba AP-115

Hardware
========

CPU   Qualcomm Atheros QCA9558
RAM   256MB DDR2
FLASH 2x 16M SPI-NOR (Macronix MX25L12805D)
WIFI  Qualcomm Atheros QCA9558
      Atheros AR9590

Installation
============

1. Attach to the serial console of the AP-105.
   Interrupt autoboot and change the U-Boot env.

   $ setenv rb_openwrt "setenv ipaddr 192.168.1.1;
     setenv serverip 192.168.1.66;
     netget 0x80060000 ap115.bin; go 0x80060000"
   $ setenv fb_openwrt "bank 1;
     cp.b 0xbf100040 0x80060000 0x10000; go 0x80060000"
   $ setenv bootcmd "run fb_openwrt"
   $ saveenv

2. Load the OpenWrt initramfs image on the device using TFTP.
   Place the initramfs image as "ap105.bin" in the TFTP server
   root directory, connect it to the AP and make the server reachable
   at 192.168.1.66/24.

   $ run rb_openwrt

3. Once OpenWrt booted, transfer the sysupgrade image to the device
   using scp and use sysupgrade to install the firmware.

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit 1b467a902ec9b8bf29805c6928627e8bbad0f14c)