perf tools: Display perf_event_attr::namespaces debug info

perf tools: Display perf_event_attr::namespaces debug info

Display namespaces bit in -vv debug display:

  $ perf record -vv --namespaces ...
  ...
  perf_event_attr:
    size                             112
    ...
    namespaces                       1

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180107160356.28203-3-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>