Metrics have a field where the groups they belong to are listed like
the following from
tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json:

        "MetricGroup": "PGO;TmaL1;TopdownL1;tma_L1_group",
        "MetricName": "tma_frontend_bound",

The metric groups are shown in 'perf list' like the following where
TopdownL1 is a metric group:

TopdownL1:
  tma_backend_bound
       [This category represents fraction of slots where no uops are being
        delivered due to a lack of required resources for accepting new uops
        in the Backend]
  tma_bad_speculation
       [This category represents fraction of slots wasted due to incorrect
        speculations]
  tma_frontend_bound
       [This category represents fraction of slots where the processor's
        Frontend undersupplies its Backend]
  tma_retiring
       [This category represents fraction of slots utilized by useful work
        i.e. issued uops that eventually get retired]

This patch adds support for a new json file in each model directory
called metricgroups.json that comprises a dictionary containing
entries that map from a metric group to a description:

{
...
    "TopdownL1": "Metrics for top-down breakdown at level 1",
...
}

perf list is then updated to support this changing the above output
to:

  TopdownL1: [Metrics for top-down breakdown at level 1]

Committer notes:

Added a (int) cast to the ARRAY_SIZE() introduced in this patch to
address:

  /tmp/build/perf-tools-next/pmu-events/pmu-events.c: In function ‘describe_metricgroup’:
  /var/home/acme/git/perf-tools-next/tools/include/linux/kernel.h:102:25: error: overflow in conversion from ‘long unsigned int’ to ‘int’ changes value from ‘18446744073709551615’ to ‘-1’ [-Werror=overflow]
    102 | #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
        |                         ^
  /tmp/build/perf-tools-next/pmu-events/pmu-events.c:61603:29: note: in expansion of macro ‘ARRAY_SIZE’
  61603 |         int low = 0, high = ARRAY_SIZE(metricgroups) - 1;
        |                             ^~~~~~~~~~
  cc1: all warnings being treated as errors
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20230517173805.602113-15-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>