IB/hfi1, rdmavt: Move SGE state helper routines into rdmavt

To improve code reuse, add small SGE state helper routines to rdmavt_mr.h.
Leverage these in hfi1, including refactoring of hfi1_copy_sge.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Brian Welty <brian.welty@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>