clockevents: Restructure clock_event_device members

Group the hot path members of struct clock_event_device together so we
have a better cache line footprint. Make it cacheline aligned.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Link: http://lkml.kernel.org/r/%3C20110518210136.223607682%40linutronix.de%3E