sched: fix !CONFIG_SCHEDSTATS build failure

Stephen Rothwell reported this linux-next build failure with !CONFIG_SCHEDSTATS:

| In file included from kernel/sched.c:1703:
| kernel/sched_fair.c: In function 'adaptive_gran':
| kernel/sched_fair.c:1324: error: 'struct sched_entity' has no member named 'avg_wakeup'

The start_runtime and avg_wakeup metrics are now not just for statistics,
but also for scheduling - so they always need to be available. (Also
move out the nr_migrations fields - for future perfcounters usage.)

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -1031,6 +1031,10 @@ struct sched_entity {
 	u64			last_wakeup;
 	u64			avg_overlap;
 
+	u64			start_runtime;
+	u64			avg_wakeup;
+	u64			nr_migrations;
+
 #ifdef CONFIG_SCHEDSTATS
 	u64			wait_start;
 	u64			wait_max;
@@ -1046,10 +1050,6 @@ struct sched_entity {
 	u64			exec_max;
 	u64			slice_max;
 
-	u64			start_runtime;
-	u64			avg_wakeup;
-
-	u64			nr_migrations;
 	u64			nr_migrations_cold;
 	u64			nr_failed_migrations_affine;
 	u64			nr_failed_migrations_running;