LinuxKPI: 802.11: adjust the hw_scan channel list

Until net80211 will grow proper scan offload with the various options
needed and will allow switching the scan engine try to improve the
situation if we are doing a hw_scan and the device supports
SINGLE_SCAN_ON_ALL_BANDS. In that case create the channel list from
our device information of supported channels rather than from the
net80211 scan list. Filter out currently unsupported bands.

While the general "scan EBUSY" problem remains at least in my local
testing I am seeing a lot more 2 and 5 GHz band results rather than
being stuck on a single band (as was also often the case with iwm for
me in the past).

Tested by: rene (previous version)
MFC after: 3 days