dt-bindings: PCI: tegra: Add device tree support for Tegra194

Add support for Tegra194 PCIe controllers. These controllers are based
on Synopsys DesignWare core IP.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>