perf evsel: Move and globalize perf_evsel__find_pmu() and perf_evsel__is_aux_event()

perf evsel: Move and globalize perf_evsel__find_pmu() and perf_evsel__is_aux_event()

Move and globalize 2 functions from the auxtrace specific sources so
that they can be reused.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/20200401101613.6201-13-adrian.hunter@intel.com
[ Move to pmu.c, as moving to evsel.h breaks the python binding ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>