wl12xx: Enable AP-mode

Indicate support for the NL80211_IFTYPE_AP interface mode to enable AP
mode operation.

Disable 11a when operating in AP-mode (unsupported for now).

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>