media: imx-mipi-csis: Use v4l2_subdev_enable_streams()

To support sources that implement the .enable_streams() and
.disable_streams() operations, replace the manual calls to the subdev
.s_stream() operation with the v4l2_subdev_enable_streams() and
v4l2_subdev_disable_streams() helpers. The helpers fall back to
.s_stream() if the source doesn't implement the new operations, so
backward compatibility is preserved.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>