perf sched: Implement multidimensional sorting

Implement multidimensional sorting on perf sched so that
you can sort either by number of switches, latency average,
latency maximum, runtime.

perf sched -l -s avg,max  (this is the default)

-----------------------------------------------------------------------------------
 Task              |  Runtime ms | Switches | Average delay ms | Maximum delay ms |
-----------------------------------------------------------------------------------
 gnome-power-man   |    0.113 ms |        1 | avg: 4998.531 ms | max: 4998.531 ms |
 xfdesktop         |    1.190 ms |        7 | avg:  136.475 ms | max:  940.933 ms |
 xfce-mcs-manage   |    2.194 ms |       22 | avg:   38.534 ms | max:  735.174 ms |
 notification-da   |    2.749 ms |       31 | avg:   27.436 ms | max:  731.791 ms |
 xfce4-session     |    3.343 ms |       28 | avg:   26.796 ms | max:  734.891 ms |
 xfwm4             |    3.159 ms |       22 | avg:   12.406 ms | max:  241.333 ms |
 xchat             |   42.789 ms |      214 | avg:   11.886 ms | max:  100.349 ms |
 xfce4-terminal    |    5.386 ms |       22 | avg:   11.414 ms | max:  241.611 ms |
 firefox           |  151.992 ms |      123 | avg:    9.543 ms | max:  153.717 ms |
 xfce4-panel       |   24.324 ms |       47 | avg:    8.189 ms | max:  242.352 ms |
 :5090             |    6.932 ms |      111 | avg:    8.131 ms | max:  102.665 ms |
 events/0          |    0.758 ms |       12 | avg:    1.964 ms | max:   21.879 ms |
 Xorg              |  280.558 ms |      340 | avg:    1.864 ms | max:   99.526 ms |
 geany             |   63.391 ms |      295 | avg:    1.099 ms | max:    9.334 ms |
 reiserfs/0        |    0.039 ms |        2 | avg:    0.854 ms | max:    1.487 ms |
 kondemand/0       |    8.251 ms |      245 | avg:    0.691 ms | max:   34.372 ms |

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>