perf trace beauty: Print O_RDONLY when (flags & O_ACCMODE) == 0

perf trace beauty: Print O_RDONLY when (flags & O_ACCMODE) == 0

And there are more flags, to match strace's output.

 openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3

Also to help with regression tests.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-ofovpmvdli3bwch30936xn7t@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>