soc/tegra: pmc: Expose USB regmap to all SoCs

All Tegra SoCs prior to Tegra186 have USB power controls within the Power
Management controller. These controls need to be configured by USB driver.
Expose the regmap to these SoCs.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>