[media] omap3isp: preview: Simplify configuration parameters access

Instead of using a large switch/case statement to return offsets to and
sizes of individual preview engine parameters in the parameters and
configuration structures, store the information in the update_attrs
table and use it at runtime.

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