IB/qib: Remove create and free mad agents

Get rid of create and free mad agent from the driver and use rdmavt
version.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>