vmstate: add no_migrate flag to VMStateDescription

This allows to easily tag devices as non-migratable,
so any attempt to migrate a virtual machine with the
device in question active will make migration fail.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/hw.h

@@ -324,6 +324,7 @@ typedef struct VMStateSubsection {
 
 struct VMStateDescription {
     const char *name;
+    int unmigratable;
     int version_id;
     int minimum_version_id;
     int minimum_version_id_old;

savevm.c

@@ -1234,6 +1234,7 @@ int vmstate_register_with_alias_id(DeviceState *dev, int instance_id,
     se->opaque = opaque;
     se->vmsd = vmsd;
     se->alias_id = alias_id;
+    se->no_migrate = vmsd->unmigratable;
 
     if (dev && dev->parent_bus && dev->parent_bus->info->get_dev_path) {
         char *id = dev->parent_bus->info->get_dev_path(dev);