perf data: Clean up use_stdio and structures

perf data: Clean up use_stdio and structures

use_stdio was associated with struct perf_data and not perf_data_file
meaning there was implicit use of fd rather than fptr that may not be
safe. For example, in perf_data_file__write. Reorganize perf_data_file
to better abstract use_stdio, add kernel-doc and more consistently use
perf_data__ accessors so that use_stdio is better respected.

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>