[media] omap3isp: Add support for the Device Tree

Add the ISP device to omap3 DT include file and add support to the driver to
use it.

Also obtain information on the external entities and the ISP configuration
related to them through the Device Tree in addition to the platform data.

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