s390x/css: ccw-0 enforces count > 0

Type-0 ccws need to have a count > 0 for any command other than TIC.
Generate a channel-program check if this is not the case.

Reviewed-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>