arm64: dts: tegra210: Add power-domains for xHCI

Populate the power-domain properties for the xHCI device for Tegra210.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>