perf report: Display perf.data header info

perf report: Display perf.data header info

Display more header info from perf.data file, following values:

  $ perf report -i perf.data --header-only
  ...
  # header version : 1
  # data offset    : 424
  # data size      : 3364280
  # feat offset    : 3364704

It's handy for debuging.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@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/20180307155020.32613-3-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>