phy: tegra: xusb: Add usb3 port fake support on Tegra210

On Tegra210, usb2 only otg/peripheral ports dont work in device mode.
They need an assosciated usb3 port to work in device mode. Identify
an unused usb3 port and assign it as a fake USB3 port to USB2 only
port whose mode is otg/peripheral.

Based on work by BH Hsieh <bhsieh@nvidia.com>.

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>