hrtimer: removing all ur callback modes, fix hotplug

Impact: fix hrtimer locking (reported by lockdep) in the CPU hotplug case

This addition fixes the hotplug locking issue on my machine

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>