perf stat: Add transaction flag (-T) support for s390

The 'perf stat' command line flag -T to display transaction counters is
currently supported for x86 only.

Add support for s390. It is based on the metrics flag -M transaction
using the architecture dependent JSON files. This requires a metric
named "transaction" in the JSON files for the platform.

Introduce a new function metricgroup__has_metric() to check for the
existence of a metric_name transaction.

As suggested by Andi Kleen, this is the new approach to support
transactions counters. Other architectures will follow.

Output before:

  [root@p23lp27 perf]# ./perf stat -T -- sleep 1
  Cannot set up transaction events
  [root@p23lp27 perf]#

Output after:

  [root@s35lp76 perf]# ./perf stat -T -- ~/mytesttx 1 >/tmp/111

   Performance counter stats for '/root/mytesttx 1':

                   1      tx_c_tend           #     13.0 transaction
                   1      tx_nc_tend
                  11      tx_nc_tabort
                   0      tx_c_tabort_special
                   0      tx_c_tabort_no_special

         0.001070109 seconds time elapsed

  [root@s35lp76 perf]#

Suggested-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20180626071701.58190-1-tmricht@linux.ibm.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>