usb: host: tegra: Locate a PHY via standard API

Use devm_get_phy_by_phandle to get a PHY device instead of the custom
Tegra functions.

Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>