perf metrics: Compute unmerged uncore metrics individually

When merging counts from multiple uncore PMUs the metric is only
computed for the metric leader. When merging/aggregation is disabled,
prior to this patch just the leader's metric would be computed. Fix
this by computing the metric for each PMU.

On a SkylakeX:
Before:
```
$ perf stat -A -M memory_bandwidth_total -a sleep 1

 Performance counter stats for 'system wide':

CPU0               82,217      UNC_M_CAS_COUNT.RD [uncore_imc_0] #      9.2 MB/s  memory_bandwidth_total
CPU18                   0      UNC_M_CAS_COUNT.RD [uncore_imc_0] #      0.0 MB/s  memory_bandwidth_total
CPU0               61,395      UNC_M_CAS_COUNT.WR [uncore_imc_0]
CPU18                   0      UNC_M_CAS_COUNT.WR [uncore_imc_0]
CPU0                    0      UNC_M_CAS_COUNT.RD [uncore_imc_1]
CPU18                   0      UNC_M_CAS_COUNT.RD [uncore_imc_1]
CPU0                    0      UNC_M_CAS_COUNT.WR [uncore_imc_1]
CPU18                   0      UNC_M_CAS_COUNT.WR [uncore_imc_1]
CPU0               81,570      UNC_M_CAS_COUNT.RD [uncore_imc_2]
CPU18             113,886      UNC_M_CAS_COUNT.RD [uncore_imc_2]
CPU0               62,330      UNC_M_CAS_COUNT.WR [uncore_imc_2]
CPU18              66,942      UNC_M_CAS_COUNT.WR [uncore_imc_2]
CPU0               75,489      UNC_M_CAS_COUNT.RD [uncore_imc_3]
CPU18              27,958      UNC_M_CAS_COUNT.RD [uncore_imc_3]
CPU0               55,864      UNC_M_CAS_COUNT.WR [uncore_imc_3]
CPU18              38,727      UNC_M_CAS_COUNT.WR [uncore_imc_3]
CPU0                    0      UNC_M_CAS_COUNT.RD [uncore_imc_4]
CPU18                   0      UNC_M_CAS_COUNT.RD [uncore_imc_4]
CPU0                    0      UNC_M_CAS_COUNT.WR [uncore_imc_4]
CPU18                   0      UNC_M_CAS_COUNT.WR [uncore_imc_4]
CPU0               75,423      UNC_M_CAS_COUNT.RD [uncore_imc_5]
CPU18             104,527      UNC_M_CAS_COUNT.RD [uncore_imc_5]
CPU0               57,596      UNC_M_CAS_COUNT.WR [uncore_imc_5]
CPU18              56,777      UNC_M_CAS_COUNT.WR [uncore_imc_5]
CPU0        1,003,440,851 ns   duration_time

       1.003440851 seconds time elapsed
```

After:
```
$ perf stat -A -M memory_bandwidth_total -a sleep 1

 Performance counter stats for 'system wide':

CPU0               88,968      UNC_M_CAS_COUNT.RD [uncore_imc_0] #      9.5 MB/s  memory_bandwidth_total
CPU18                   0      UNC_M_CAS_COUNT.RD [uncore_imc_0] #      0.0 MB/s  memory_bandwidth_total
CPU0               59,498      UNC_M_CAS_COUNT.WR [uncore_imc_0]
CPU18                   0      UNC_M_CAS_COUNT.WR [uncore_imc_0]
CPU0                    0      UNC_M_CAS_COUNT.RD [uncore_imc_1] #      0.0 MB/s  memory_bandwidth_total
CPU18                   0      UNC_M_CAS_COUNT.RD [uncore_imc_1] #      0.0 MB/s  memory_bandwidth_total
CPU0                    0      UNC_M_CAS_COUNT.WR [uncore_imc_1]
CPU18                   0      UNC_M_CAS_COUNT.WR [uncore_imc_1]
CPU0               88,635      UNC_M_CAS_COUNT.RD [uncore_imc_2] #      9.5 MB/s  memory_bandwidth_total
CPU18             117,975      UNC_M_CAS_COUNT.RD [uncore_imc_2] #     11.5 MB/s  memory_bandwidth_total
CPU0               60,829      UNC_M_CAS_COUNT.WR [uncore_imc_2]
CPU18              62,105      UNC_M_CAS_COUNT.WR [uncore_imc_2]
CPU0               82,238      UNC_M_CAS_COUNT.RD [uncore_imc_3] #      8.7 MB/s  memory_bandwidth_total
CPU18              22,906      UNC_M_CAS_COUNT.RD [uncore_imc_3] #      3.6 MB/s  memory_bandwidth_total
CPU0               53,959      UNC_M_CAS_COUNT.WR [uncore_imc_3]
CPU18              32,990      UNC_M_CAS_COUNT.WR [uncore_imc_3]
CPU0                    0      UNC_M_CAS_COUNT.RD [uncore_imc_4] #      0.0 MB/s  memory_bandwidth_total
CPU18                   0      UNC_M_CAS_COUNT.RD [uncore_imc_4] #      0.0 MB/s  memory_bandwidth_total
CPU0                    0      UNC_M_CAS_COUNT.WR [uncore_imc_4]
CPU18                   0      UNC_M_CAS_COUNT.WR [uncore_imc_4]
CPU0               83,595      UNC_M_CAS_COUNT.RD [uncore_imc_5] #      8.9 MB/s  memory_bandwidth_total
CPU18             110,151      UNC_M_CAS_COUNT.RD [uncore_imc_5] #     10.5 MB/s  memory_bandwidth_total
CPU0               56,540      UNC_M_CAS_COUNT.WR [uncore_imc_5]
CPU18              53,816      UNC_M_CAS_COUNT.WR [uncore_imc_5]
CPU0        1,003,353,416 ns   duration_time
```

Signed-off-by: Ian Rogers <irogers@google.com>                                  |
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Kaige Ye <ye@kaige.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240221070754.4163916-2-irogers@google.com