IB/qib: Setup notify free/create mad agent callbacks for rdmavt

Qib needs to be notified when mad agents are created and freed, there is
some counter maintenance that needs to be performed. Add those callbacks at
registration time with rdmavt.

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