perf bench uprobe empty: Add entry attaching an empty BPF program

perf bench uprobe empty: Add entry attaching an empty BPF program

Using libbpf and a BPF skel:

  # perf bench uprobe all
  # Running uprobe/baseline benchmark...
  # Executed 1,000 usleep(1000) calls
       Total time: 1,055,618 usecs

   1,055.618 usecs/op
  # Running uprobe/empty benchmark...
  # Executed 1,000 usleep(1000) calls
       Total time: 1,057,146 usecs +1,528 to baseline

   1,057.146 usecs/op
  #

Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andre Fredette <anfredet@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Dave Tucker <datucker@redhat.com>
Cc: Derek Barbosa <debarbos@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/20230719204910.539044-5-acme@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>