[USB] EHCI updates

Update periodic schedule scanning
	- fix shutdown sometimes-hangs (Bernd Porr)
	- resolve the "whole frame at once" FIXME
	- try harder to avoid rescanning
	- don't delegate interrupt qh handling to a buggy helper routine
	- describe more of the relevant iso tuning parameters

One-liners:
	- URB_NO_INTERRUPT hint affects ISO
	- show correct data toggle in sysfs debug files
	- FIXME is resolved by Linus' 20msec delay