Use machine/timespec.h to separate timespec definition.

Bug: 18627763
Change-Id: Ib1c406320f0ecc3705d19183a48f986cdf57c279
diff --git a/libc/include/sched.h b/libc/include/sched.h
index 4f9e2a6..930dd7c 100644
--- a/libc/include/sched.h
+++ b/libc/include/sched.h
@@ -28,10 +28,9 @@
 #ifndef _SCHED_H_
 #define _SCHED_H_
 
-#include <sys/cdefs.h>
-#include <sys/time.h>
-
 #include <linux/sched.h>
+#include <machine/timespec.h>
+#include <sys/cdefs.h>
 
 __BEGIN_DECLS