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

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>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39063 3c298f89-4303-0410-b956-a3cf2f4a3e73