dt-bindings: can: rcar_canfd: document r8a774b1 support

Document the support for rcar_canfd on R8A774B1 SoC devices.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1570717560-7431-3-git-send-email-fabrizio.castro@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>