Add a parent Object to Object instances, and track the parent-children relationships. Children are bound to the same thread as their parent, and moving an Object to a thread automatically moves all its children. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>