x86/x2apic: Convert to CPU hotplug state machine

x86/x2apic: Convert to CPU hotplug state machine

Install the callbacks via the state machine and let the core invoke
the callbacks on the already online CPUs.

Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Anna-Maria Gleixner <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mathias Krause <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>