iwlwifi: pcie: let the Manageability Engine know when we leave

When the driver is unload, the Manageability Engine should
know about that - send an event to inform it about this
event.

Reviewed-by: Reuven Borok <reuven.borok@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>