tracing: use generic __stringify

Impact: clean up

This removes the custom made STR(x) macros in the tracer and uses
the generic __stringify macro instead.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/kernel/trace/events.c b/kernel/trace/events.c
index f2509cb..9fc918d 100644
--- a/kernel/trace/events.c
+++ b/kernel/trace/events.c
@@ -2,9 +2,7 @@
  * This is the place to register all trace points as events.
  */
 
-/* someday this needs to go in a generic header */
-#define __STR(x) #x
-#define STR(x) __STR(x)
+#include <linux/stringify.h>
 
 #include <trace/trace_events.h>