perf bpf: Move perf_event_output() from stdio.h to bpf.h

perf bpf: Move perf_event_output() from stdio.h to bpf.h

So that we don't always carry that __bpf_output__ map, leaving that to
the scripts wanting to use that facility.

'perf trace' will be changed to look if that map is present and only
setup the bpf-output events if so.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-azwys8irxqx9053vpajr0k5h@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>