media: imx.rst: add it to v4l-drivers book

Avoid the following warning when building documentation:
	checking consistency... /devel/v4l/patchwork/Documentation/media/v4l-drivers/imx.rst:: WARNING: document isn't included in any toctree

While here, avoid placing all driver authors at just one line at
the html/pdf output.

Acked-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>