USB: EHCI: introduce high-res timer

This patch (as1572) begins the conversion of ehci-hcd over to using
high-resolution timers rather than old-fashioned low-resolution kernel
timers.  This reduces overhead caused by timer roundoff on systems
where HZ is smaller than 1000.  Also, the new timer framework
introduced here is much more logical and easily extended than the
ad-hoc approach ehci-hcd currently uses for timers.

An hrtimer structure is added to ehci_hcd, along with a bitflag array
and an array of ktime_t values, to keep track of which timing events
are pending and what their expiration times are.

Only the infrastructure for the timing operations is added in this
patch.  Later patches will add routines for handling each of the
various timing events the driver needs.  In some cases the new hrtimer
handlers will replace the existing handlers for ehci-hcd's kernel
timers; as this happens the old timers will be removed.  In other
cases the new timing events will replace busy-wait loops.

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

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