perf bench: Add benchmark for evlist open/close operations

This new benchmark finds the total time that is taken to open, mmap,
enable, disable, munmap, close an evlist (time taken for new,
create_maps, config, delete is not counted in).

The evlist can be configured as in perf-record using the
-a,-C,-e,-u,--per-thread,-t,-p options.

The events can be duplicated in the evlist to quickly test performance
with many events using the -n options.

Furthermore, also the number of iterations used to calculate the
statistics is customizable.

Examples:
- Open one dummy event system-wide:

  $ sudo ./perf bench internals evlist-open-close
    Number of cpus:       4
    Number of threads:    1
    Number of events:     1 (4 fds)
    Number of iterations: 100
    Average open-close took: 613.870 usec (+- 32.852 usec)

- Open the group '{cs,cycles}' on CPU 0

  $ sudo ./perf bench internals evlist-open-close -e '{cs,cycles}' -C 0
    Number of cpus:       1
    Number of threads:    1
    Number of events:     2 (2 fds)
    Number of iterations: 100
    Average open-close took: 8503.220 usec (+- 252.652 usec)

- Open 10 'cycles' events for user 0, calculate average over 100 runs

  $ sudo ./perf bench internals evlist-open-close -e cycles -n 10 -u 0 -i 100
    Number of cpus:       4
    Number of threads:    328
    Number of events:     10 (13120 fds)
    Number of iterations: 100
    Average open-close took: 180043.140 usec (+- 2295.889 usec)

Committer notes:

Replaced a deprecated bzero() call with designated initialized zeroing.

Added some missing evlist allocation checks, one noted by Riccardo on
the mailing list.

Minor cosmetic changes (sent in private).

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20210809201101.277594-1-rickyman7@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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