tracing: fix document references

When moving documents to Documentation/trace/, I forgot to
grep Kconfig to find out those references.

Signed-off-by: Li Zefan <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: Pekka Paalanen <[e-mail]>
Cc: [e-mail]
LKML-Reference: <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

kernel/trace/Kconfig

···
 	  and profile kernel code.
 
 	  This requires an userspace application to use. See
-	  Documentation/vm/kmemtrace.txt for more information.
+	  Documentation/trace/kmemtrace.txt for more information.
 
 	  Saying Y will make the kernel somewhat larger and slower. However,
 	  if you disable kmemtrace at run-time or boot-time, the performance
···
 	  implementation and works via page faults. Tracing is disabled by
 	  default and can be enabled at run-time.
 
-	  See Documentation/tracers/mmiotrace.txt.
+	  See Documentation/trace/mmiotrace.txt.
 	  If you are not helping to develop drivers, say N.
 
 config MMIOTRACE_TEST