USB: PHY: tegra: Get rid of instance number to differentiate PHY type

Tegra20 USB has 3 PHY instances:
Instance 1 and 3 are UTMI. Instance 2 is ULPI.

As instance number was used to differentiate ULPI from UTMI,
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>
[swarren: moved assignment of phy->is_ulpi_phy into this patch out
of next patch.]
Signed-off-by: Stephen Warren <swarren@nvidia.com>