Describe CVBS video input through analog video decoder ADV7180
connected to video input interface VIN4.

The video input signal path is shared with HDMI video input, and
selected by on-board switches SW-53 and SW-54 with CVBS input selected
by the default switches configuration.
Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>