perf tools: Add all matching dynamic sort keys for field name

When a perf.data file has multiple events, it's likely to be similar
(tracepoint) events.  In that case, they might have same field name so
add all of them to sort keys instead of bailing out.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1451991518-25673-2-git-send-email-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>