wl12xx: Add channel 14 to list of supported 2ghz channels

Channel 14 is only supported in Japan (JP country code in regdb).  The
FW limits tranmissions to CCK only on this channel.

Tested in both STA and AP modes to work correctly.

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