perf stat: Add --metric-only support for -A

Add metric only support for -A too. This requires a new print function
that prints the metrics in the right order.

v2: Fix manpage
v3: Simplify nrcpus computation

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1457049458-28956-7-git-send-email-andi@firstfloor.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>