Utilise the clang-format header sort to provide a regex based pattern match for our header inclusion coding style. The rules are updated to match as closely as possible the existing practices and the documentation is updated accordingly. Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com> Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>