v4l2object: mark jpeg as parsed

v4l2object: mark jpeg as parsed

Assuming that V4L2 CAPTURE devices always use one buffer per JPEG image, we can
always mark JPEGs provided by a V4L2 element as parsed.

The V4L2 elements require that JPEG images sent to V4L2 OUTPUT devices must
always be parsed.

This is necessary to link a V4L2 CAPTURE device with a V4L2 OUTPUT device
without explicitly marking the stream as parsed or adding a jpegparse into the
pipeline.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4247>