In preparation for multiple streams support prepare to allow sub-classing the Stream class by removing the 'final' specifier from the class definition and make its private members protected. Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>