perf stat: Add ScaleUnit to {cpu,task}-clock JSON description

This changes the output of the event like below.  In fact, that's the
output it used to have before the JSON conversion.

Before:
  $ perf stat -e task-clock true

   Performance counter stats for 'true':

             313,848      task-clock                       #    0.290 CPUs utilized

         0.001081223 seconds time elapsed

         0.001122000 seconds user
         0.000000000 seconds sys

After:
  $ perf stat -e task-clock true

   Performance counter stats for 'true':

                0.36 msec task-clock                       #    0.297 CPUs utilized

         0.001225435 seconds time elapsed

         0.001268000 seconds user
         0.000000000 seconds sys

Reviewed-by: Ian Rogers <irogers@google.com>
Fixes: 9957d8c8 ("perf jevents: Add common software event json")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>