vdpa/mlx5: reuse event queues

vdpa/mlx5: reuse event queues

To speed up queue creation time, event QP and CQ will create only once.
Each virtq creation will reuse same event QP and CQ.

Because FW will set event QP to error state during virtq destroy,
need modify event QP to RESET state, then modify QP to RTS state as
usual. This can save about 1.5ms for each virtq creation.

After SW QP reset, QP pi/ci all become 0 while CQ pi/ci keep as
previous. Add new variable qp_ci to save SW QP ci. Move QP pi
independently with CQ ci.

Add new function mlx5_vdpa_drain_cq to drain CQ CQE after virtq
release.

Signed-off-by: Yajun Wu <yajunw@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>