dt-bindings: media: video-interfaces: add support for dual edge sampling

Some devices support sampling of the parallel data at both edges of the
interface pixel clock in order to reduce the pixel clock by two.
Use the pclk-sample property to reflect this feature in the device tree.

Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>