vdpa/mlx5: Rename control VQ workqueue to vdpa wq

A subesequent patch will use the same workqueue for executing other
work not related to control VQ. Rename the workqueue and the work queue
entry used to convey information to the workqueue.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210909123635.30884-3-elic@nvidia.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>