vdpa: move SVQ vring features check to net/

vdpa: move SVQ vring features check to net/

The next patches will start control SVQ if possible. However, we don't
know if that will be possible at qemu boot anymore.

Since the moved checks will be already evaluated at net/ to know if it
is ok to shadow CVQ, move them.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20221215113144.322011-8-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>