make seccomp zerocost in schedule

This follows a suggestion from Chuck Ebbert on how to make seccomp
absolutely zerocost in schedule too.  The only remaining footprint of
seccomp is in terms of the bzImage size that becomes a few bytes (perhaps
even a few kbytes) larger, measure it if you care in the embedded.

Signed-off-by: Andrea Arcangeli <andrea@cpushare.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/seccomp.c

@@ -74,6 +74,9 @@ long prctl_set_seccomp(unsigned long seccomp_mode)
 	if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
 		current->seccomp.mode = seccomp_mode;
 		set_thread_flag(TIF_SECCOMP);
+#ifdef TIF_NOTSC
+		disable_TSC();
+#endif
 		ret = 0;
 	}