This adds clock references to the USB part of the device tree for U-Boot,
and marks USB1 as supporting legacy mode (which we disable in the driver).

The USB timing information may vary between boards sometimes, but for
now we hard-code it in C. This is because all current T2x boards use
the same values, we will deal with T3x later and we first need to agree
on the format for this timing information in the fdt and may in fact
decide that it has no place there.

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