iwlagn: implement loading a new firmware file type

The old firmware file type does not allow indicating
any firmware capabilities, which we frequently want
to make things easier.

This implements a new firmware type that is based on
a TLV structure, and adds a TLV for the maximum length
of probe requests in scans.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>