vdpa/mlx5: Decouple virtqueue callback from struct mlx5_vdpa_virtqueue

vdpa/mlx5: Decouple virtqueue callback from struct mlx5_vdpa_virtqueue

Instead, define an array of struct vdpa_callback on struct mlx5_vdpa_net
and use it to store callbacks for any virtqueue provided. This is
required due to the fact that callback configurations arrive before feature
negotiation. With control VQ and multiqueue introduced next we want to
save the information until after feature negotiation where we know the
CVQ index.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210823052123.14909-4-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>