media: staging: media: imx: imx7-media-csi: Drop V4L2 events support

The only event that the driver allows subscribing to,
V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR, is never generated. Drop events
support.

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>