s390: sclp base support

s390: sclp base support

This adds a more generic infrastructure for handling Service-Call
requests on s390. Currently we only support a small subset of Read
SCP Info directly in target-s390x. This patch provides the base
infrastructure for supporting more commands and moves Read SCP
Info.
In the future we could add additional commands for hotplug, call
home and event handling.

Signed-off-by: Heinz Graalfs <graalfs@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>