[media] omap3isp: preview: Add crop support on the sink pad

The crop rectangle takes the preview engine internal cropping
requirements into account. The smallest allowable margins are 14 columns
and 8 rows when reading from memory, and 18 columns and 8 rows when
processing data on the fly from the CCDC.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>