iwlwifi: mvm: add a scan timeout for regular scans

If something goes wrong with the firmware and we never get a scan
complete notification, we stay stuck forever.  In order to avoid this
situation, add a timeout and trigger an NMI if it expires before
receiving the notification., so we can clean things up.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>