ar71xx: add kernel support for the TL-WA801ND v2 board

Patch to add kernel support for the TP-LINK WA801ND v2

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Patchwork: http://patchwork.openwrt.org/patch/4500/
[juhosg:
  - the TL-WA801ND v2 does not have a sliding switch, it uses a push button
    for WPS instead. Use the tl_mr3420v2_gpio_keys array to reflect that,
  - rename kernel patch]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
SVN-Revision: 39063