This adds an enum to the load tile buffer that forces the alpha channel to be set to 1. This will be required later to load RGBX formats. Reviewed-by: Iago Toral Quiroga <itoral@igalia.com> Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7816>