Some Intel xhci(4) controllers don't fully power down unless they've seen

Some Intel xhci(4) controllers don't fully power down unless they've seen
a "save state" command.  So use that command when we suspend (and don't
reset the controller at that point such that it doesn't forget about it).
Note that on resume we don't restore the state.  Instead we just reset
the controller and bring it up from scratch.  There isn't much state to
save anyway since we detach all USB devices when we suspend.

ok mlarkin@, deraadt@