function_trace_stop is no longer used to disable function tracing.
This means that archs are no longer limited if it does not support
checking this variable in the mcount trampoline.

No need to use the list_func for archs that do not support this
obsolete method.
Acked-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>