perf record: Add readable output for callchain debug

Adding people readable output for callchain debug, to get following '-v'
output:

  $ perf record -v -g ls
  callchain: type DWARF
  callchain: stack dump size 4096
  ...

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1391427883-13443-3-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/perf.h

@@ -251,7 +251,8 @@ void pthread__unblock_sigwinch(void);
 enum perf_call_graph_mode {
 	CALLCHAIN_NONE,
 	CALLCHAIN_FP,
-	CALLCHAIN_DWARF
+	CALLCHAIN_DWARF,
+	CALLCHAIN_MAX
 };
 
 struct record_opts {