ar71xx: add kernel support for ZyXEL NBG 6716

With this patch OpenWRT supports the following on the ZyXEL NBG 6716:
-WiFi 2G (ath9k)
-WiFi 5G (ath10k)
-NAND flash
-2 Ethernet interfaces
-USB 2.0
-LEDs including switch
-reasonale defaults at first boot

Signed-off-by: André Valentin <avalentin@marcant.net>
Patchwork: http://patchwork.openwrt.org/patch/5101/


[juhosg:
  - rename and refresh kernel patch,
  - fix a few typos,
  - change button key codes,
  - use zyxel prefix in LED names]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

SVN-Revision: 40499