[S390] cio: introduce css_eval_scheduled

Use css_eval_scheduled to determine if all scheduled subchannel
evaluation is finished. Wait for this value to be 0 in the
channel subsystem init function.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>