IB/rdmavt: Consolidate dma ops in rdmavt.

This patch adds dma functions to rdmavt. The source is hfi1's version of
dma.c which will be removed by a subsequent hfi1 patch.

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