perf util: Allocate time slices buffer according to number of comma

Previously we use a magic number 10 to limit the number of time slices.
It's not very good.

This patch creates a new function perf_time__range_alloc() to allocate
time slices buffer. The number of buffer entries is determined by the
number of comma in string but at least it will allocate one entry even
if no comma is found.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1515596433-24653-7-git-send-email-yao.jin@linux.intel.com


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