perf header: Add DIR_FORMAT feature to describe directory data

perf header: Add DIR_FORMAT feature to describe directory data

The data files layout is described by HEADER_DIR_FORMAT feature.
Currently it holds only version number (1):

     uint64_t version;

The current version holds only version value (1) means that data files:

  - Follow the 'data.*' name format.

  - Contain raw events data in standard perf format as read from kernel
    (and need to be sorted)

Future versions are expected to describe different data files layout
according to special needs.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20190308134745.5057-6-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>