trace: Allow ftrace_dump() to be called from modules

Add an EXPORT_SYMBOL_GPL() so that rcutorture can dump the trace buffer
upon detection of an RCU error.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

kernel/trace/trace.c

@@ -4775,6 +4775,7 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
 {
 	__ftrace_dump(true, oops_dump_mode);
 }
+EXPORT_SYMBOL_GPL(ftrace_dump);
 
 __init static int tracer_alloc_buffers(void)
 {