dt-bindings: phy: tegra-xusb: Add usb-role-switch

Add usb-role-switch property for Tegra210 and Tegra186 platforms. This
entry is used by XUSB pad controller driver to register for role changes
for OTG/Peripheral capable USB 2 ports.

Signed-off-by: Nagarjuna Kristam <nkristam@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>