iwlwifi: move D3_CFG_COMPLETE handling into DVM

The MVM firmware doesn't communicate this way, it instead
assumes D3 configuration is complete after a specific host
command (which must be last) has been sent. Handling this
bit thus belongs into the firmware API code, i.e. DVM.

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