pixel-formats: Add XYUV8888 format

XYUV8888 support was added to gl-renderer in 30104bd89a, but not to
pixel-formats. Oops.

Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/pixel-formats.c

@@ -505,6 +505,9 @@ static const struct pixel_format_info pixel_format_table[] = {
 		.num_planes = 3,
 		.chroma_order = ORDER_VU,
 	},
+	{
+		DRM_FORMAT(XYUV8888),
+	},
 };
 
 WL_EXPORT const struct pixel_format_info *