mach/timex.h is about to be dropped so don't use symbols defined in
there. For ixp4xx there is a suitable substitute for IXP4XX_TIMER_FREQ,
i.e. a global and exported variable that holds the same value.
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>