dt-bindings: phy: Add NVIDIA Tegra XUSB pad controller binding

The NVIDIA Tegra XUSB pad controller provides a set of pads, each with a
set of lanes that are used for PCIe, SATA and USB.

A binding exists for the XUSB pad controller already, but it turned out
not to be flexible enough to describe all aspects of the controller. In
particular, the addition of XUSB support (for SuperSpeed USB) has shown
that the existing binding is no longer suitable. Mark the old binding
as deprecated and link to the new binding.

Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>