IB/rdmavt: Add data structures and routines for table driven post send

Add flexibility for driver dependent operations in post send
because different drivers will have differing post send
operation support.

This includes data structure definitions to support a table
driven scheme along with the necessary validation routine
using the new table.

Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Jianxin Xiong <jianxin.xiong@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>