perf stat: Print topology/time headers with --metric-only

perf stat: Print topology/time headers with --metric-only

When --metric-only is enabled there were no headers for the topology in
interval mode.  Also when headers were printed they were on a separate
line.

Before:

  $ perf stat  --metric-only  -A -I 1000 -a
    1.001038376     frontend cycles idle insn per cycle  stalled cycles per insn branch-misses of all branches
    1.001038376 CPU0   123.54%               0.23           5.29                    7.61%
    1.001038376 CPU1   137.78%               0.24           5.13                   10.07%
    1.001038376 CPU2    64.48%               0.22           5.50                    6.84%

After:

  $ perf stat  --metric-only  -A -I 1000 -a
    1.001111114 CPU0    82.46%               0.32           2.60                    7.64%
    1.001111114 CPU1   126.63%               0.02          42.83                    0.15%
    1.001111114 CPU2   193.54%               0.32           2.59                    6.92%

v2: Move all headers on a single line

Reported-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1464119559-17203-3-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>