perf stat: Align cgroup names

perf stat: Align cgroup names

We don't know how long cgroup name is, but at least we can align short
ones like below.

  $ perf stat -a --for-each-cgroup system.slice,user.slice true

   Performance counter stats for 'system wide':

           0.13 msec cpu-clock         system.slice  #    0.010 CPUs utilized
              4      context-switches  system.slice  #   31.989 K/sec
              1      cpu-migrations    system.slice  #    7.997 K/sec
              0      page-faults       system.slice  #    0.000 /sec
        450,673      cycles            system.slice  #    3.604 GHz             (92.41%)
        161,216      instructions      system.slice  #    0.36  insn per cycle  (92.41%)
         32,678      branches          system.slice  #  261.332 M/sec           (92.41%)
          2,628      branch-misses     system.slice  #    8.04% of all branches (92.41%)
          14.29 msec cpu-clock         user.slice    #    1.163 CPUs utilized
             35      context-switches  user.slice    #    2.449 K/sec
             12      cpu-migrations    user.slice    #  839.691 /sec
             57      page-faults       user.slice    #    3.989 K/sec
     49,683,026      cycles            user.slice    #    3.477 GHz             (99.38%)
    110,790,266      instructions      user.slice    #    2.23  insn per cycle  (99.38%)
     24,552,255      branches          user.slice    #    1.718 G/sec           (99.38%)
        127,779      branch-misses     user.slice    #    0.52% of all branches (99.38%)

    0.012289431 seconds time elapsed

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20221114230227.1255976-10-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>