Display metric expression itself when --details is specified.

Current list with no details:

  # perf list metrics
  ...
  TopDownL1:
    IPC
         [Instructions Per Cycle (per logical thread)]
    SLOTS
         [Total issue-pipeline slots]
  ...

Detailed output with metric formula:

  # perf list --details metrics
  ...
  TopDownL1:
    IPC
         [Instructions Per Cycle (per logical thread)]
         [inst_retired.any / cpu_clk_unhalted.thread]
    SLOTS
         [Total issue-pipeline slots]
         [4*(( cpu_clk_unhalted.thread_any / 2 ) if #smt_on else cycles)]
  ...
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20190213123246.4015-6-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>