USB: PHY: tegra: get rid of instance number to differentiate legacy controller

Tegra20 USB has 3 PHY instances. Instance 0 is based on
legacy PHY interface and other two are standard interfaces.

As instance number was used to differentiate legacy from
standard interfaces, used DT param to get this info and
processed accordingly.

Signed-off-by: Venu Byravarasu <vbyravarasu@nvidia.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>