cpu: Call cpu_synchronize_post_init() from CPUClass.realize() if hotplugged

... to synchronize CPU state to KVM

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>