Add an sclp event for "cpu was hot plugged".  This allows Qemu to deliver an
SCLP interrupt to the guest stating that the requested cpu hotplug was
completed.
Signed-off-by: NJason J. Herne <jjherne@us.ibm.com>
Reviewed-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>