wl12xx: increase number of allowed SSIDs in sched_scan

The latest firmware supports up to 16 SSIDs in the scheduled scan
lists.  Increase the number we report to cfg80211 and increase the
min/max dwell time to 30 and 60 TUs respectively, because otherwise we
don't have the time to send the probes for all SSIDs.

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