s390x/migration: migrate CPU state

This patch provides the cpu save information for dumps and later life
migration and enables migration of the CPU state. The code is based on
earlier work from Christian Borntraeger and Jason Herne.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
[provide cpu_post_load()]
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
CC: Andreas Faerber <afaerber@suse.de>
CC: Christian Borntraeger <borntraeger@de.ibm.com>
CC: Jason J. Herne <jjherne@us.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
s390x/virtio-ccw: fix vhost-scsi intialization

The vhost-scsi-ccw backend is of type VHostSCSICcw, not VirtIOSCSICcw.

This fixes a segfault when invoking

    qemu-system-s390x -device vhost-scsi-ccw,?

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>