ath79: add support for ALLNET ALL-WAP02860AC

ath79: add support for ALLNET ALL-WAP02860AC

ALLNET ALL-WAP02860AC is a dual-band wireless access point.

Specification
SoC: Qualcomm Atheros QCA9558
RAM: 128 MB DDR2
Flash: 16 MB SPI NOR
WIFI: 2.4 GHz 3T3R integrated
      5 GHz 3T3R QCA9880 Mini PCIe card
Ethernet: 1x 10/100/1000 Mbps AR8035-A, PoE capable (802.3at)
LEDS: 5x, which four are GPIO controlled
Buttons: 1x GPIO controlled
UART: 4 pin header near Mini PCIe card, starting count from white
      triangle on PCB
      1. VCC 3.3V, 2. GND, 3. TX, 4. RX
      baud: 115200, parity: none, flow control: none

MAC addresses
Calibration data does not contain valid MAC addresses.
The calculated MAC addresses are chosen in accordance with OEM firmware.

Because of:
a) constrained environment (SNMP) when connecting through Telnet
   or SSH,
b) hard-coded kernel and rootfs sizes,
c) checksum verification of kerenel and rootfs images in bootloder,

creating factory image accepted by OEM web interface is difficult,
therefore, to install OpenWrt on this device UART connection is needed.
The teardown is simple, unscrew four screws to disassemble the casing,
plus two screws to separate mainboard from the casing.
Before flashing, be sure to have a copy of factory firmware, in case You
wish to revert to original firmware.

Installation
1. Prepare TFTP server with OpenWrt initramfs-kernel image.
2. Connect to LAN port.
3. Connect to UART port.
4. Power on the device and when prompted to stop autoboot, hit any key.
5. Alter U-Boot environment with following commands:
    setenv failsafe_boot bootm 0x9f0a0000
    saveenv
6. Adjust "ipaddr" and "serverip" addresses in U-Boot environment, use
   'setenv' to do that, then run following commands:
    tftpboot 0x81000000 <openwrt_initramfs-kernel_image_name>
    bootm 0x81000000
7. Wait about 1 minute for OpenWrt to boot.
8. Transfer OpenWrt sysupgrade image to /tmp directory and flash it
   with:
    sysupgrade -n /tmp/<openwrt_sysupgrade_image_name>
9. After flashing, the access point will reboot to OpenWrt. Wait few
   minutes, until the Power LED stops blinking, then it's ready for
   configuration.

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>
[add MAC address comment to commit message]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>