tracing: Do not do anything special with tracepoint_string when tracing is disabled

tracing: Do not do anything special with tracepoint_string when tracing is disabled

When CONFIG_TRACING is not enabled, there's no reason to save the trace
strings either by the linker or as a static variable that can be
referenced later. Simply pass back the string that is given to
tracepoint_string().

Had to move the define to include/linux/tracepoint.h so that it is still
visible when CONFIG_TRACING is not set.

Link: http://lkml.kernel.org/p/1406318733-26754-2-git-send-email-nicolas.pitre@linaro.org
Suggested-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>