dt-bindings: Add Tegra234 PCIe clocks and resets

Add the clocks and resets used by the PCIe hardware found on
Tegra234 SoCs.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>