media: imx.rst: Add example media graphs

Add the media graph topologies for the i.MX6Q SabreSD and SabreAuto.
This makes it easier to understand the topology and follow the
entity descriptions in the following sections.

Also clarify that the SabreSD and SabreLite media pipeline config examples
are for the i.MX6Q boards.

Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>