perf evlist: Factor perf_evlist__(enable|disable) functions

perf evlist: Factor perf_evlist__(enable|disable) functions

Use perf_evsel__(enable|disable) functions in perf_evlist__(enable|disable)
functions in order to centralize ioctl enable/disable calls. This way we
eliminate 2 places calling directly ioctl.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1449133606-14429-4-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>