perf bench: Modify bench/bench-messaging.c to adopt unified output formatting

This patch modifies bench/bench-messaging.c to adopt
unified output formatting: --format option.

Usage example:

 % ./perf bench sched messaging              # with no style
 specify (20 sender and receiver processes per group)
 (10 groups == 400 processes run)

        Total time:1.431 sec

 % ./perf bench --format=simple sched messaging # specified
 simple 1.431

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: <1257808802-9420-4-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>