perf evsel: Allow specifying a file to output in perf_evsel__print_ip

As this function will be used in 'perf trace'.

Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/n/tip-8x297v9utnxq77onikevvlse@git.kernel.org


[ Split from a larger patch ]
Signed-off-by: Milian Wolff <milian.wolff@kdab.com>