perf kvm: Update documentation to reflect new changes

Update documentation for new sorting and option '--stdio'.

Reviewed-by: James Clark <[e-mail]>
Signed-off-by: Leo Yan <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: John Garry <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-kvm.txt

···
   events.
 
   'perf kvm stat report' reports statistical data which includes events
-  handled time, samples, and so on.
+  handled sample, percent_sample, time, percent_time, max_t, min_t, mean_t.
 
   'perf kvm stat live' reports statistical data in a live mode (similar to
   record + report but with statistical data updated live at a given display
···
 :GMEXAMPLESUBCMD: top
 include::guest-files.txt[]
 
+--stdio:: Use the stdio interface.
+
 -v::
 --verbose::
 	Be more verbose (show counter open errors, etc).
···
 -k::
 --key=<value>::
        Sorting key. Possible values: sample (default, sort by samples
-       number), time (sort by average time).
+       number), percent_sample (sort by sample percentage), time
+       (sort by average time), precent_time (sort by time percentage),
+       max_t (sort by maximum time), min_t (sort by minimum time), mean_t
+       (sort by mean time).
 -p::
 --pid=::
     Analyze events only for given process ID(s) (comma separated list).