For the common evsel list traversal, so that it becomes more compact.

Use the opportunity to start ditching the 'perf_' from 'perf_evlist__',
as discussed, as the whole conversion touches a lot of places, lets do
it piecemeal when we have the chance due to other work, like in this
case.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-qnkx7dzm2h6m6uptkfk03ni6@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>