Add CANFD binding documentation for Renesas R9A07G043 (RZ/G2UL) SoC.

Link: https://lore.kernel.org/all/20220423130743.123198-1-biju.das.jz@bp.renesas.comSigned-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>