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/kernel/sched.c b/kernel/sched.c
index 3ac3d7a..8f433fe 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -899,7 +899,7 @@
 	return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
 }
 
-static const unsigned long long time_sync_thresh = 100000;
+unsigned long long time_sync_thresh = 100000;
 
 static DEFINE_PER_CPU(unsigned long long, time_offset);
 static DEFINE_PER_CPU(unsigned long long, prev_cpu_time);