drm: bridge: Add dual_link field to the drm_bridge_timings structure

Extend the drm_bridge_timings structure with a new dual_link field to
indicate that the bridge's input bus carries data on two separate
physical links. The first use case is LVDS dual-link mode where even-
and odd-numbered pixels are transferred on separate LVDS links.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Tested-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>