perf ordered_events: Introduce reinit()

'perf record' will use this when outputting multiple perf.data files.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1460535673-159866-2-git-send-email-wangnan0@huawei.com


Signed-off-by: He Kuang <hekuang@huawei.com>
[ Split from larger patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>