perf sort: Separate out memory-specific sort keys

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>