USB: ehci: Elide I/O watchdog on NEC parts

I've been running with this patch on my Niagara2 boxes for some time
and have not seen any ill effects yet.  Maybe we can stash this into
the USB tree to get exposure for some time in -next and if anything
crops up we can simply revert?

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>