kprobes, x86: Prohibit probing on thunk functions and restore

thunk/restore functions are also used for tracing irqoff etc.
and those are involved in kprobe's exception handling.
Prohibit probing on them to avoid kernel crash.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20140417081726.26341.3872.stgit@ltc230.yrl.intra.hitachi.co.jp
Signed-off-by: Ingo Molnar <mingo@kernel.org>