ARM: tegra: parameterize common XUSB code

There are some differences between the Tegra124 and Tegra210 XUSB padctl
code. So far, the common XUSB padctl code only supports Tegra124. Add
some parameters etc. so that it can work for both chips.

This also allows moving Tegra124's process_nodes() into the common file;
something that would have requires edits during the move if done in the
previous commit.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>