perf sort: Separate out memory-specific sort keys

Since they're used only for perf mem, separate out them to a different
dimension so that normal user cannot access them by any chance.

For global/local weights, I'm not entirely sure to place them into the
memory dimension.  But it's the only user at this time.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1364991979-3008-3-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-report.c

@@ -871,6 +871,8 @@ repeat:
 			fprintf(stderr, "branch and mem mode incompatible\n");
 			goto error;
 		}
+		sort__mode = SORT_MODE__MEMORY;
+
 		/*
 		 * if no sort_order is provided, then specify
 		 * branch-mode specific order