arm64: tegra: Add PCIe node for Tegra186

Tegra186 has three PCIe controllers, which can be operated
in 401, 211 or 111 lane combinations. Add DT support for
PCIe controllers.

Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Tested-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>