perf bench: Print both of prefaulted and no prefaulted results by default

After applying this patch, perf bench mem memcpy prints
both of prefualted and without prefaulted score of memcpy().

New options --no-prefault and --only-prefault are added
to print single result, mainly for scripting usage.

Usage example:

 | mitake@X201i:~/linux/.../tools/perf% ./perf bench mem memcpy -l 500MB
 | # Running mem/memcpy benchmark...
 | # Copying 500MB Bytes ...
 |
 |      634.969014 MB/Sec
 |        4.828062 GB/Sec (with prefault)
 | mitake@X201i:~/linux/.../tools/perf% ./perf bench mem memcpy -l 500MB --only-prefault
 | # Running mem/memcpy benchmark...
 | # Copying 500MB Bytes ...
 |
 |        4.705192 GB/Sec (with prefault)
 | mitake@X201i:~/linux/.../tools/perf% ./perf bench mem memcpy -l 500MB --no-prefault
 | # Running mem/memcpy benchmark...
 | # Copying 500MB Bytes ...
 |
 |      642.725568 MB/Sec

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: h.mitake@gmail.com
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: Ma Ling <ling.ma@intel.com>
Cc: Zhao Yakui <yakui.zhao@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andi Kleen <andi@firstfloor.org>
LKML-Reference: <1290668693-27068-1-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>