Extend the V4L2Subdevice API with stream support for the functions that get and set formats and selection rectangles. Add a Stream structure to identify a subdev pad and stream, and use it to extend the V4L2Subdevice functions that get and set formats and selection rectangles with stream support. To preserve the existing pad-based API, implement overloaded functions that wrap the new stream-based API. This allows callers that are not stream-aware to use a simpler pad-based API, instead of having to explicitly set the stream number to 0 in all API calls. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>