rxe will hold a refcount on the IB device as long as CQ objects exist,
this causes destruction of a rxe device to hang if the CQ pool has any
cached CQs since they are being destroyed after the refcount must go to
zero.

Treat the CQ pool like a client and create/destroy it before/after all
other clients. No users of CQ pool can exist past a client remove call.

Link: https://lore.kernel.org/r/e8a240aa-9e9b-3dca-062f-9130b787f29b@acm.org
Fixes: c7ff819a ("RDMA/core: Introduce shared CQ pool API")
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>