iwlwifi: mvm: refactor resume from WoWLAN code

To be able to add more logic to the resume code, refactor it a bit,
moving some status checking/reporting logic into a new function.
The locking becomes a bit odd (one of the new functions now unlocks
the mutex) but this will be required to call new mac80211 APIs in
there later.

Reviewed-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>