Implemented in hw/s390x/s390-virtio-hcall.c, so let's move it to the
right header file.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170913132417.24384-6-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>