iwlwifi: mvm: add common scan params to thw iwl_mvm_scan_params struct

Many parameters are common for all scans.  Instead of parsing the
cfg80211 scan and sched scan requests differently in each flow, move
the parsing outside of the API/scan-type specific functions.  In this
way, we only need to differentiate between scan types once.
Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>