drm: rcar-du: Add interlaced feature flag

Upcoming implementations of the R-Car DU have removed support for
interlaced display pipelines. Provide a means to determine this based on
the feature flags of the hardware configuration structs.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>