[media] v4l: omap3isp: Drop platform data support

Platforms using the OMAP3 ISP have all switched to DT, drop platform
data support.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>