iwlwifi: trans: allow skipping scheduler hardware config

In a later patch, the hardware configuration will be moved to
firmware. Prepare for this by allowing hardware configuration
in the transport to be skipped by not passing a configuration
on enable and passing configure_scd=false on disable.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>