Remove unmapped/freed memory regions from the object property list.

This commit fixes the following issues:
- Any unmapped/free'd memory regions (MemoryRegion instances) are not
  removed from the object property linked list of its owner (which is
  always qdev_get_machine(uc)). This issue makes adding new memory
  mapping by calling mem_map() or mem_map_ptr() slower as more and more
  memory pages are mapped and unmapped - yes, even if those memory pages
  are unmapped, they still impact the speed of future memory page
  mappings due to this issue.
- FlatView is not reconstructed after a memory region is freed during
  unmapping, which leads to a use-after-free the next time a new memory
  region is mapped in address_space_update_topology().

qemu/include/qom/object.h

@@ -810,6 +810,8 @@ ObjectProperty *object_property_add(Object *obj, const char *name,
 
 void object_property_del(struct uc_struct *uc, Object *obj, const char *name, Error **errp);
 
+void object_property_del_child(struct uc_struct *uc, Object *obj, Object *child, Error **errp);
+
 /**
  * object_property_find:
  * @obj: the object