IB/rdmavt: Add misc dev register functionality

There are a number of minor things that should be set by rdmavt rather
than by the drivers. Now that rdmavt has solidified in its design we can
go ahead and clean up this stuff.

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>