USB: EHCI: resolve some unlikely races

This patch (as1589) resolves some unlikely races involving system
shutdown or controller death in ehci-hcd:

	Shutdown races with both root-hub resume and controller
	resume.

	Controller death races with root-hub suspend.

A new bitflag is added to indicate that the controller has been shut
down (whether for system shutdown or because it died).  Tests are
added in the suspend and resume pathways to avoid reactivating the
controller after any sort of shutdown.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>