perf stat: Additional verbose details for <not supported> events

perf stat: Additional verbose details for <not supported> events

If an event shows as "<not supported>" in perf stat output, in verbose
mode add the strerror output to help diagnose the issue.

Consider:
```
$ perf stat -e cycles,data_read,instructions true

 Performance counter stats for 'true':

           357,457      cycles:u
   <not supported> MiB  data_read:u
           156,182      instructions:u                   #    0.44  insn per cycle

       0.001250315 seconds time elapsed

       0.001283000 seconds user
       0.000000000 seconds sys
```

To understand why the data_read uncore event failed you can run it
again with -v option.  This change adds detailed message about the
error and suggestion how to fix it potentially.

  Warning:
  data_read:u event is not supported by the kernel.
  Invalid event (data_read:u) in per-thread mode, enable system wide with '-a'.

Signed-off-by: Ian Rogers <irogers@google.com>
[ simplified the commit message ]
Signed-off-by: Namhyung Kim <namhyung@kernel.org>