perf evsel: Add own_cpus member

perf_evlist__propagate_maps() cannot easily tell if an evsel has its own
cpu map.  To make that simpler, keep a copy of the PMU cpu map and
adjust the propagation logic accordingly.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Link: http://lkml.kernel.org/r/1441699142-18905-8-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>