ARM: tegra: Implement XUSB pad controller

This controller was introduced on Tegra114 to handle XUSB pads. On
Tegra124 it is also used for PCIe and SATA pin muxing and PHY control.
Only the Tegra124 PCIe and SATA functionality is currently implemented,
with weak symbols on Tegra114.

Tegra20 and Tegra30 also provide weak symbols for these functions so
that drivers can use the same API irrespective of which SoC they're
being built for.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>