ARM: tegra: tegra124: Add XUSB pad controller

The device tree node in the SoC file contains only the resources (such
as registers, resets, ...) but none of the lane assignment information
since that's board specific and belongs in the board file.

Tested-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>