iwlwifi: mvm: Add debugfs entry to enable scan offload notification

This option enables scan offload iteration complete notification from
firmware which includes the last iteration's status and the scanned
channels from the current iteration.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>