[PATCH] sched: arch preempt notifier mechanism

This adds a general mechanism whereby a task can request the scheduler to
notify it whenever it is preempted or scheduled back in.  This allows the
task to swap any special-purpose registers like the fpu or Intel's VT
registers.

Signed-off-by: Avi Kivity <avi@qumranet.com>
[ mingo@elte.hu: fixes, cleanups ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/Kconfig.preempt

@@ -63,3 +63,6 @@ config PREEMPT_BKL
 	  Say Y here if you are building a kernel for a desktop system.
 	  Say N if you are unsure.
 
+config PREEMPT_NOTIFIERS
+	bool
+