perf trace: Add beautifier for open's flags arg

Suppressing the mode when O_CREAT not present, needs improvements on the
arg masking mechanism to be reused in openat, open_by_handle_at,
mq_open:

[root@zoo ~]# perf trace -a -e open | grep -v 'flags: RDONLY' | head -5
   147.541 ( 0.028 ms): 1188 open(filename: 0x33c17782fb, flags: CLOEXEC   ) = 23
   229.898 ( 0.020 ms): 2071 open(filename: 0x3d93c80, flags: NOATIME      ) = -1 EPERM Operation not permitted

[root@zoo ~]# perf trace -a -e open | grep CREAT
  1406.697 ( 0.024 ms): 616 open(filename: 0x7fffc3a0f910, flags: CREAT|TRUNC|WRONLY, mode: 438 ) = -1 ENOENT No such file or directory
  2032.770 ( 0.804 ms): 4354 open(filename: 0x7f33ac814368, flags: CREAT|EXCL|RDWR, mode: 384   ) = 115
^C[root@zoo ~]#

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-c7vm6klaf995qw1vqdih5t7q@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>