USB: Add the USB 2.0 extension descriptor.

This device descriptor was added by the recent USB Link Power Management (LPM)
ECN.  It indicates whether the USB device supports LPM.

This descriptor is grouped under a Binary Device Object Store (BOS) descriptor.
Update the BOS comments to indicate any USB device (not just wireless USB
devices) can implement BOS descriptors.

Signed-off-by: Sarah Sharp <sarah.a.sharp@intel.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>