PIO send context mapping is changed from per-VL to QPN based.

qp to send context mapping is done using a mapping infrastructure
similar to the current vl to sdma engine mapping.
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>