vdpa/mlx5: Ensure valid indices are provided

vdpa/mlx5: Ensure valid indices are provided

Following patches add control virtuqeue and multiqueue support. We want
to verify that the index value to callbacks referencing a virtqueue is
valid.

The logic defining valid indices is as follows:
CVQ clear: 0 and 1.
CVQ set, MQ clear: 0, 1 and 2
CVQ set, MQ set: 0..nvq where nvq is whatever provided to
_vdpa_register_device()

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210823052123.14909-5-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>