dt-bindings: can: rcar_can: Add r8a774c0 support

Document RZ/G2E (r8a774c0) SoC specific bindings.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>