perf bench: Add sched-pipe.c: Benchmark for pipe() system call

This patch adds bench/sched-pipe.c.

bench/sched-pipe.c is a benchmark program
to measure performance of pipe() system call.
This benchmark is based on pipe-test-1m.c by Ingo Molnar:

   http://people.redhat.com/mingo/cfs-scheduler/tools/pipe-test-1m.c



Example of use:

% perf bench sched pipe
  (executing 1000000 pipe operations between two tasks)

          Total time:4.499 sec
                  4.499179 usecs/op
                  222262 ops/sec

% perf bench sched pipe -s -l 1000
0.015

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: fweisbec@gmail.com
Cc: Jiri Kosina <jkosina@suse.cz>
LKML-Reference: <1257381097-4743-4-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>