perf evsel: Switch to libperf's cpumap.h

We don't need what is in perf's util/cpumap.h, just the struct cpu_map
that is in libperf's internal/cpumap.h file to cover this one case:

  tools/perf/util/evsel.h:215:27: error: dereferencing pointer to incomplete type ‘struct perf_cpu_map’
  215 |  return evsel__cpus(evsel)->nr;

So switch to libperf's cpumap.h and add some missing struct foward
declarations and include sys/types.h to get pid_t.

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-ufjkpohijti05ggk69s91ktf@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>