arm64: tegra: Add XUSB powergates on Tegra210

The Tegra210 XUSB subsystem has 3 power partitions which are XUSBA
(super-speed logic), XUSBB (USB device logic) and XUSBC (USB host
logic). Populate the device-tree nodes for these XUSB partitions.

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