perf stat: Add id into perf_stat struct

We need fast way to identify evsel as transaction event for shadow
counters computation. Currently we are using possition (in evlist) based
way.

Adding 'id' into 'struct perf_stat' so it can carry transaction event ID
and we can use it for shadow counters computations.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20150604135055.GB23625@krava.redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>