wl12xx: AP mode - support hidden SSID

If a hidden SSID is requested, generate a probe response template
containing the real SSID.

Depends on the patch "mac80211: add ssid config to bss information
in AP-mode".

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