cpu: Register VMStateDescription through CPUState In comparison to DeviceClass::vmsd, CPU VMState is split in two, "cpu_common" and "cpu", and uses cpu_index as instance_id instead of -1. Therefore add a CPU-specific CPUClass::vmsd field. Unlike the legacy CPUArchState registration, rather register CPUState. Signed-off-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Andreas Färber <afaerber@suse.de> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>