perf bench: Improve sched-message.c with more comfortable output

This patch improves sched-message.c with more comfortable output.

Change points are comment style description and
formatting numerical values and its units.

Example:

 | % perf bench sched messaging
 | # Running sched/messaging benchmark...
 | # 20 sender and receiver processes per group
 | # 10 groups == 400 processes run
 |
 |      Total time: 1.490 [sec]

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1257865442-20252-4-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>