perf evlist: Maintain evlist->all_cpus

perf evlist: Maintain evlist->all_cpus

Maintain a cpumap in the evlist that is the union of all the cpus of the
events.

This needs a cpumap merge operation, which is added together with tests.

v2:
Add tests for cpu map merge
Fix handling of duplicates
Rename _update to _merge
Factor out sorting.
Fix handling of NULL maps in merge

v3:
Add comments and empty lines to _merge

Committer testing:

  # perf test "Merge cpu map"
  52: Merge cpu map                                         : Ok
  #

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lore.kernel.org/lkml/20191121001522.180827-5-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>