phy: tegra: xusb: Add support for power supplies

Support enabling various supplies needed to provide power to the PLLs
and logic used to drive the USB, PCI and SATA pads.

Reviewed-by: JC Kuo <jckuo@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>