iwlwifi: mvm: downgrade to old power management API

Current available FW still doesn't support new PM API.
Therefore, to enable basic power management with the
existing firmware, change the API in the driver back
to the API used in the current firmware.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>