iwlwifi: pcie: add basic reference accounting

Implement the ref/unref trans ops and track both tx and
host command queues (and hold references while they
are not empty).

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>