IB/ehca: Generate flush status CQ entries

When a QP goes into error state, it is required that CQ entries with a
flush error status are delivered to the application for any
outstanding work requests.  eHCA does not do this in hardware, so this
patch adds software flush CQE generation to the ehca driver.

Whenever a QP gets into error state, it is added to the QP error list
of its respective CQ.  If the error QP list of a CQ is not empty,
poll_cq() generates flush CQEs before polling the actual CQ.

Signed-off-by: Alexander Schmidt <alexs@linux.vnet.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>