media: imx: imx7-media-csi: Disable legacy video node API

Support for the MC-centric API has been tested on the i.MX7. Enable it
for that platform. i.MX6 should be converted next.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.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+huawei@kernel.org>