staging/rdma/hfi1: Use rdmavt device allocation function

No longer do drivers need to call into the IB core to allocate the verbs
device.  Use the functionality provided by rdmavt.

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>