usb: hub: Parse and save TT details from device descriptor

A high speed hub has a special responsibility to handle full speed/
low speed devices connected on downstream ports. In this case, the
hub must isolate the high speed signaling environment from the full
speed/low speed signaling environment with the help of Transaction
Translator (TT). TT details are provided by hub descriptors and we
parse and save it to hub uclass_priv for later use.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>