media: Documentation: Reword split of sensor driver to two classes

The sensor drivers do not configure the output size of the sensors but the
entire internal pipeline. Reflect this in the documentation.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>