drm: rcar-du: Remove packed VYUY support

The Gen3 VSP used by the DU for display does not support the packed VYUY
pixel format. Gen2 VSP hardware is able to process this format, but
DU + VSP operation isn't enabled on Gen2, and VYUY isn't a strategic
format, so it can be ignored.

Remove the format from the capabilities of the DU driver.

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>