iwlwifi: mvm: allow transport sleep when FW is operational

Hold a bitmap of taken references, according to the
reference reason (e.g. down, scan).

This will allow us validate our state and add some debugfs
entries later on.

Unref the transport when the FW is fully initialized,
allowing it to go into a low power mode.

Disallow the transition to low-power while recovery is in
progress.

Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>