perf stat: Factor out event handling loop into dispatch_events()

perf stat: Factor out event handling loop into dispatch_events()

Consolidate event dispatching loops for fork, attach and system wide
monitoring use cases into common dispatch_events() function.

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/8a900bd5-200a-9b0f-7154-80a2343bfd1a@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>