perf evsel: util/evsel.h needs stdio.h as it uses FILE

And it was getting it by luck from util/cpumap.h that shouldn't be
included in util/evsel.h as it only needs what is in libperf, i.e.
struct cpu_map, that is in internal/cpumap.h, so add stdio.h before
we fix that.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-2ywx5sl031tj3zske7c7edgv@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>