phy: tegra: xusb: Add usb-phy support

For USB 2 ports that has usb-role-switch enabled, add usb-phy for
corresponding USB 2 phy. USB role changes from role switch are then
updated to corresponding host and device mode drivers via usb-phy notifier
block.

Signed-off-by: Nagarjuna Kristam <nkristam@nvidia.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
[treding@nvidia.com: rebase onto Greg's usb-next branch]
Signed-off-by: Thierry Reding <treding@nvidia.com>