iwlwifi: mvm: add unified LMAC scan API

Add new scan API that uses the same command 0x51 for both regular and
sched scan.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>