perfcounters: add task migrations counter

Impact: add new feature, new sw counter

Add a counter that counts the number of cross-CPU migrations a
task is suffering.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4c53027..2e15be8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1014,6 +1014,8 @@
 	u64			last_wakeup;
 	u64			avg_overlap;
 
+	u64			nr_migrations;
+
 #ifdef CONFIG_SCHEDSTATS
 	u64			wait_start;
 	u64			wait_max;
@@ -1029,7 +1031,6 @@
 	u64			exec_max;
 	u64			slice_max;
 
-	u64			nr_migrations;
 	u64			nr_migrations_cold;
 	u64			nr_failed_migrations_affine;
 	u64			nr_failed_migrations_running;