dt-bindings: pci: tegra: Add Tegra210 support

Add support for the PCI host controller found on Tegra210 SoCs. It is very
similar to the variant found on Tegra124, with a couple of small
differences regarding the power supplies.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Bjorn Helgaas <helgaas@kernel.org>