s390x/migration: migrate CPU state

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>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
[Cornelia Huck: tweaked cpu_post_load() comment]
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>