Improve the documentation by providing examples on how to test camera
capture on imx6q-sabresd via v4l2-ctl and Gstreamer.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Steve <Longerbeam&lt;slongerbeam@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>