iwlwifi: mvm: prevent nic to powered up at driver load

A few devices aren't allowed to be powered up at driver
load time. Add "power_up_nic_in_init" flag to iwl_cfg
structure to customize the load flow according to the
device.

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