IB/rdmavt: Add a send completion helper

This is for use by client drivers to drive
send completions into a CQ.

A new exported table allows for the mapping
of ib_wr_opcode into a ib_wc_opcode.

Reviewed-by: Ashutosh Dixit <ashutosh.dixit@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>