perf evsel: Add PERF_SAMPLE_READ sample related processing

perf evsel: Add PERF_SAMPLE_READ sample related processing

For sample with sample type PERF_SAMPLE_READ the period value is stored
in the 'struct sample_read'.

Moreover if the read format has PERF_FORMAT_GROUP, the 'struct
sample_read' contains period values for all events in the group (for
which the sample's event is a leader).

We deliver separated samples for all the values contained within the
'struct sample_read'.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-6mdm5xkrm6kypouh1c33cyys@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>