media: imx7.rst: Fix the references to the CSI multiplexer

In imx7s.dtsi the node name for the CSI multiplexer is "csi-mux", not
"csi_mux", so fix all the references in the document.

This fixes the following error when the instructions are followed:

Unable to parse link: Invalid argument (22)

While at it, provide the "media-ctl -p" output from 5.2 kernel
version, so that users can see a more updated output.

Fixes: fa88fbda ("media: imx7.rst: add documentation for i.MX7 media driver")
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>