wl12xx: add support for sched_scan filters

Implement support for filtering in scheduled scans.

With this commit we now use the match sets passed by cfg80211 to
filter on SSIDs.  Due to the nature of the wl12xx firmware API, we
don't allow SSIDs to be sent in the probe requests if they are not
going to match any of the filters.

Signed-off-by: Luciano Coelho <coelho@ti.com>