brcmfmac: add support multi-scheduled scan

This change adds support for multi-scheduled scan in the driver. It
currently relies on g-scan support in firmware and will set struct
wiphy::max_sched_scan_reqs accordingly. This is limited to 16 concurrent
requests.

The firmware currently has a limit of 64 channels that can be configured
for all requests in total regardless whether there are duplicates. So if
a request uses 35 channels there are 29 channels left for another request.
When user-space does not specify any channels cfg80211 will add all
channels defined by the wiphy instance to the request, which makes
reaching the limit rather easy for dual-band devices.

Reviewed-by: Hante Meuleman <hante.meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>