davinci: DM644x platform changes for vpfe capture

DM644x platform and board setup

This adds platform and board setup changes required to support
vpfe capture driver on DM644x

Tested video capture on DM6446 with tvp514x driver

Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Reviewed-by: David Brownell <david-b@pacbell.net>
Signed-off-by: Muralidharan Karicheri <m-karicheri2@ti.com>
Signed-off-by: Denys Dmytriyenko <denis@denix.org>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>