perf report: Support time sort key

Add a time sort key to perf report to display samples for different time
quantums separately. This allows easier analysis of workloads that
change over time, and also will allow looking at the context of samples.

% perf record ...
% perf report --sort time,overhead,symbol --time-quantum 1ms --stdio
...
     0.67%  277061.87300  [.] _dl_start
     0.50%  277061.87300  [.] f1
     0.50%  277061.87300  [.] f2
     0.33%  277061.87300  [.] main
     0.29%  277061.87300  [.] _dl_lookup_symbol_x
     0.29%  277061.87300  [.] dl_main
     0.29%  277061.87300  [.] do_lookup_x
     0.17%  277061.87300  [.] _dl_debug_initialize
     0.17%  277061.87300  [.] _dl_init_paths
     0.08%  277061.87300  [.] check_match
     0.04%  277061.87300  [.] _dl_count_modids
     1.33%  277061.87400  [.] f1
     1.33%  277061.87400  [.] f2
     1.33%  277061.87400  [.] main
     1.17%  277061.87500  [.] main
     1.08%  277061.87500  [.] f1
     1.08%  277061.87500  [.] f2
     1.00%  277061.87600  [.] main
     0.83%  277061.87600  [.] f1
     0.83%  277061.87600  [.] f2
     1.00%  277061.87700  [.] main

Committer notes:

Rename 'time' argument to hist_time() to htime to overcome this in older
distros:

  cc1: warnings being treated as errors
  util/hist.c: In function 'hist_time':
  util/hist.c:251: error: declaration of 'time' shadows a global declaration
  /usr/include/time.h:186: error: shadowed declaration is here

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20190311144502.15423-4-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>