ath79: create Aruba AP-105 APBoot compatible image

ath79: create Aruba AP-105 APBoot compatible image

Alter the Aruba AP-105 image generation process so OpenWrt can be loaded
with the vendor Aruba APBoot.

This works by prepending the OpenWrt LZMA loader to the uImage and
jumping directly to the loader. Aruba does not offer bootm on these
boards.

This approach keeps compatibility to devices which had their U-Boot
replaced. Both bootloaders can boot the same image.

The same modification is most likely also possible for the Aruba AP-175.

With this patch, new installations do not require replacing the
bootloader and can be performed from the serial console without opening
the case.

Installation
------------

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

   $ setenv apb_rb_openwrt "setenv ipaddr 192.168.1.1;
     setenv serverip 192.168.1.66;
     netget 0x84000000 ap105.bin; go 0x84000040"
   $ setenv apb_fb_openwrt "cp.b 0xbf040000 0x84000000 0x10000;
     go 0x84000040"
   $ setenv bootcmd "run apb_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 apb_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 e11d00d44c66b1534fbc399fda55951cd0a2168a)