IB/core: Add rdma_cap_opa_ah to expose opa address handles

rdma_cap_opa_ah(..) enables core components to check if the
corresponding port supports OPA extended addressing.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>