s390x: Add more Ultravisor command structure definitions

They are needed in the new UV tests.

As we now extend the size of the query struct, we need to set the
length in the UV guest query test to a constant instead of using
sizeof.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>