perf header: Don't pass struct perf_file_section to process_##_feat

perf header: Don't pass struct perf_file_section to process_##_feat

struct perf_file_section is used in process_##_feat as container for
size and offset in the file descriptor. These attributes are meaninful
in pipe-mode but struct perf_file_section is not.

Add offset and size variables to struct feat_fd to store
perf_file_section's values in file-mode. Later on, the same variables
can be reused for pipe-mode.

This patch does not change behavior.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
Acked-by: David Ahern <dsahern@gmail.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Simon Que <sque@chromium.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20170718042549.145161-10-davidcc@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>