dt-bindings: arm: tegra: Add NVIDIA Tegra234 CBB 2.0 binding

Add device-tree binding documentation to represent the Control Backbone
(CBB) version 2.0 used on Tegra234 SoCs.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>