x86: add notrace annotations to vsyscall.

Add the notrace annotations to the vsyscall functions - there we are
not in kernel context yet, so the tracer function cannot (and must not)
be called.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>