USB: split hub.h into ch11.h and merge-in hcd.h

Base on inputs from Alan Stern, split the hub.h header into:
- new ch11.h header (most of it) containing constants and
  structures from chapter 11 of the USB 2.0 spec.
- a small remaining part being merged into hcd.h.

Signed-of-by: Eric Lescouet <eric@lescouet.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>