media: staging: media: imx: imx7-media-csi: Fold imx_media_dev into imx7_csi

Now that the driver doesn't use any helper that relies on the
imx_media_dev structure anymore, merge the three fields of the
imx_media_dev structure directly in the imx7_csi structure. Update all
the users accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>