IB/ehca: Add PMA support

This patch enables ehca to redirect any PMA queries to the
actual PMA QP.

Signed-off-by: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
Reviewed-by: Joachim Fenkes <fenkes@de.ibm.com>
Reviewed-by: Christoph Raisch <raisch@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>