perf auxtrace: Move evlist__enable_event_idx() to auxtrace.c

perf auxtrace: Move evlist__enable_event_idx() to auxtrace.c

evlist__enable_event_idx() is used only by auxtrace. Move it to auxtrace.c
in preparation for making it even more auxtrace specific.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lore.kernel.org/lkml/20220506122601.367589-5-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>