perf header: Display missing features

Display missing features in header info, like:

  $ perf report --header-only
  # ========
  # captured on: Mon Oct 10 09:39:47 2016
  ...
  # missing features: HEADER_TRACING_DATA HEADER_CPU_TOPOLOGY ...

To help in diagnosing problems.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-bh5gp84gobdmyl345dcp64se@git.kernel.org


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