USB: Turn on auto-suspend for USB 3.0 hubs.

Now that USB 3.0 hub remote wakeup on port status changes is enabled,
and USB 3.0 device remote wakeup is handled in the USB core properly,
let's turn on auto-suspend for all USB 3.0 hubs.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>