sched: make clock sync tunable by architecture code

make time_sync_thresh tunable to architecture code.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 698b5a4..54c9ca2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -158,6 +158,8 @@
 }
 #endif
 
+extern unsigned long long time_sync_thresh;
+
 /*
  * Task state bitmask. NOTE! These bits are also
  * encoded in fs/proc/array.c: get_task_state().