wlcore: make scan scan configuration functions more generic

18xx and 12xx have different scan APIs. In 18xx,
the scan and the sched scan use the same struct.

Prepare the scan configuration functions to it, by taking
more generic params (e.g. ieee80211_channel) instead of
specific structs/requests.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>