It all operates on the evsels in the session's evlist, so move it to the
evlist layer to make it useful to tools not using perf_session, just
evlists, like 'perf trace' in live mode.

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-9oc53gnfi53vg82fvolkm85g@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>