perf tools: Use perf_mmap way to detect aux mmap

We will move this code to libperf shortly, so we need to free it of
'struct auxtrace_mmap' usage, because it won't be available in libperf
(for now).

The perf_event_mmap_page::aux_size is set when the aux mmap is mapped,
so the check is equivalent.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20191007125344.14268-9-jolsa@kernel.org


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