perf evsel: Add iterator to iterate over events ordered by CPU

Add some common code that is needed to iterate over all events
in CPU order. Used in followon patches

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20191121001522.180827-6-andi@firstfloor.org


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