dt-bindings: PCI: tegra234: Add ECAM support

Add support for ECAM aperture that is only supported for Tegra234
devices.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Co-developed-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>