USB: Disable auto-suspend for USB 3.0 hubs.

USB 3.0 devices have a slightly different suspend sequence than USB
2.0/1.1 devices.  There isn't support for USB 3.0 device suspend yet, so
make khubd leave autosuspend disabled for USB 3.0 hubs.  Make sure that
USB 3.0 roothubs still have autosuspend enabled, since that path in the
xHCI driver works fine.

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