media: mc: Add num_links flag to media_pad

[ Upstream commit baeddf94 ]

Maintain a counter of the links connected to a pad in the media_pad
structure. This helps checking if a pad is connected to anything, which
will be used in the pipeline building code.

Cc: stable@vger.kernel.org # 6.1
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>