vhost scsi: Allow user to control num virtqueues

We are currently hard coded to always create 128 IO virtqueues, so this
adds a modparam to control it. For large systems where we are ok with
using memory for virtqueues it allows us to add up to 1024. This limit
was just selected becuase that's qemu's limit.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20220708030525.5065-3-michael.christie@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>