arm64: tegra: Add CPU idle states properties for Tegra210

Add idle states properties for generic ARM CPU idle driver. This
includes a cpu-sleep state which is the power down state of CPU cores.

Signed-off-by: Joseph Lo <josephl@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>