phy: tegra: xusb: Add vbus override support on Tegra210

Tegra XUSB device control driver needs to control vbus override
during its operations, add API for the support.

Signed-off-by: Nagarjuna Kristam <nkristam@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>