perf top: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set

perf top: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set

When I execute 'perf top' without HAVE_LIBBPF_SUPPORT, there exists the
following segmentation fault, skip the side-band event setup to fix it,
this is similar with commit 1101c872c8c7 ("perf record: Skip side-band
event setup if HAVE_LIBBPF_SUPPORT is not set").

  [yangtiezhu@linux perf]$ ./perf top
  <SNIP>
  perf: Segmentation fault
  Obtained 6 stack frames.
  ./perf(sighandler_dump_stack+0x5c) [0x12011b604]
  [0xffffffc010]
  ./perf(perf_mmap__read_init+0x3e) [0x1201feeae]
  ./perf() [0x1200d715c]
  /lib64/libpthread.so.0(+0xab9c) [0xffee10ab9c]
  /lib64/libc.so.6(+0x128f4c) [0xffedc08f4c]
  Segmentation fault
  [yangtiezhu@linux perf]$

I use git bisect to find commit b38d85ef49cf ("perf bpf: Decouple
creating the evlist from adding the SB event") is the first bad commit,
so also add the Fixes tag.

Committer testing:

First build perf explicitely disabling libbpf:

  $ make NO_LIBBPF=1 O=/tmp/build/perf -C tools/perf install-bin && perf test python

Now make sure it isn't linked:

  $ perf -vv | grep -w bpf
                   bpf: [ OFF ]  # HAVE_LIBBPF_SUPPORT
  $
  $ nm ~/bin/perf | grep libbpf
  $

And now try to run 'perf top':

  # perf top
  perf: Segmentation fault
  -------- backtrace --------
  perf[0x5bcd6d]
  /lib64/libc.so.6(+0x3ca6f)[0x7fd0f5a66a6f]
  perf(perf_mmap__read_init+0x1e)[0x5e1afe]
  perf[0x4cc468]
  /lib64/libpthread.so.0(+0x9431)[0x7fd0f645a431]
  /lib64/libc.so.6(clone+0x42)[0x7fd0f5b2b912]
  #

Applying this patch fixes the issue.

Fixes: b38d85ef49cf ("perf bpf: Decouple creating the evlist from adding the SB event")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.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>
Cc: Xuefeng Li <lixuefeng@loongson.cn>
Link: http://lore.kernel.org/lkml/1597753837-16222-1-git-send-email-yangtiezhu@loongson.cn
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>