proc: move /proc/schedstat boilerplate to kernel/sched_stats.h

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
diff --git a/kernel/sched.c b/kernel/sched.c
index d906f72..5a70189 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -55,6 +55,7 @@
 #include <linux/cpuset.h>
 #include <linux/percpu.h>
 #include <linux/kthread.h>
+#include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/sysctl.h>
 #include <linux/syscalls.h>