[PATCH] x86_64: Don't allow kprobes on __switch_to

kprobes cannot deal with the funny calling conventions when it
runs on a different stack when it returns. If someone wants
to instrument context switch they can add a probe to schedule()
instead.

Cc: jkenisto@us.ibm.com, prasanna@in.ibm.com

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>