iwlwifi: mvm: select the MAC address according to priority

For family 8000 products, the driver should take the MAC
address from the mac_override section and only if this
section is empty it should take it from the HW section.

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>