dt-bindings: can: rcar_can: Convert to json-schema

Convert the Renesas R-Car CAN Controller Device Tree binding
documentation to json-schema.

Document missing properties.
Update the example to match reality.

Link: https://lore.kernel.org/r/561c35648e22a3c1e3b5477ae27fd1a50da7fe98.1620323639.git.geert+renesas@glider.be
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>