iwlwifi: mvm: simplify calculating scan dwells and other timing values

Remove timing values from iwl_mvm_scan_params and use defines and
arrays of values instead.

While at that fix few values and corner cases and align all OSs
to ChromeOS values.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Reviewed-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>