perf python: Fix up the build on architectures without HAVE_KVM_STAT_SUPPORT

Noticed while building on a raspbian arm 32-bit system.

There was also this other case, fixed by adding a missing util/stat.h
with the prototypes:

  /tmp/tmp.MbiSHoF3dj/perf-6.12.0-rc3/tools/perf/util/python.c:1396:6: error: no previous prototype for ‘perf_stat__set_no_csv_summary’ [-Werror=missing-prototypes]
   1396 | void perf_stat__set_no_csv_summary(int set __maybe_unused)
        |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /tmp/tmp.MbiSHoF3dj/perf-6.12.0-rc3/tools/perf/util/python.c:1400:6: error: no previous prototype for ‘perf_stat__set_big_num’ [-Werror=missing-prototypes]
   1400 | void perf_stat__set_big_num(int set __maybe_unused)
        |      ^~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

In other architectures this must be building due to some lucky indirect
inclusion of that header.

Fixes: 9dabf400 ("perf python: Switch module to linking libraries from building source")
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZxllAtpmEw5fg9oy@x1


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