dt-bindings: can: rcar_can: Add r8a7742 support

Document RZ/G1H (r8a7742) SoC specific bindings. The R8A7742 CAN module
is identical to R-Car Gen2 family.

No driver change is needed due to the fallback compatible value
"renesas,rcar-gen2-can".

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Link: https://lore.kernel.org/r/20200816190732.6905-3-prabhakar.mahadev-lad.rj@bp.renesas.com


Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>