dt-bindings: can: rcar_canfd: document r8a774c0 support

Document the support for rcar_canfd on R8A774C0 SoC devices.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
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>