media: imx7.rst: Provide an example for imx6ull-evk capture

imx6ull-evk has a parallel OV5640 sensor.

Provide an example for imx6ull-evk capture to improve the document.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>