perf stat: Add 'identifier' flag to 'struct perf_stat_config'

Add 'identifier' flag to 'struct perf_stat_config' to carry the info
whether to use PERF_SAMPLE_IDENTIFIER for events.

This makes create_perf_stat_counter() independent.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180830063252.23729-6-jolsa@kernel.org


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