perf stat: Always separate stalled cycles per insn

perf stat: Always separate stalled cycles per insn

The "stalled cycles per insn" is appended to "instructions" when the CPU
has this hardware counter directly. We should always make it a separate
line, which also aligns to the output when we hit the "if (total &&
avg)" branch.

Before:

  $ sudo perf stat --all-cpus --field-separator , --log-fd 1 -einstructions,cycles -- sleep 1
  4565048704,,instructions,64114578096,100.00,1.34,insn per cycle,,
  3396325133,,cycles,64146628546,100.00,,

After:

  $ sudo ./tools/perf/perf stat --all-cpus --field-separator , --log-fd 1 -einstructions,cycles -- sleep 1
  6721924,,instructions,24026790339,100.00,0.22,insn per cycle
  ,,,,,0.00,stalled cycles per insn
  30939953,,cycles,24025512526,100.00,,

Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/20190517221039.8975-1-xiyou.wangcong@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>