drm: rcar-du: Add more formats to DRM_MODE_BLEND_PIXEL_NONE support

Add additional pixel formats for which blending is disabled when
DRM_MODE_BLEND_PIXEL_NONE is set.

Refactor the fourcc selection into a separate function to handle the
increased number of formats.

Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>