soc/tegra: pmc: Don't power-up XUSB power-domains

Now that the Tegra xHCI driver manages the XUSB power-domains itself,
remove the code to power-up the power-domains used by the xHCI device
from the PMC driver on boot.

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