perf mem: Only initialize memory event for recording

It's needless to initialize memory events for reporting, this patch
moves memory event initialization for only recording.  Furthermore,
the change allows to parse perf data on cross platforms, e.g. perf
tool can report result properly even the machine doesn't support
the memory events.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20201106094853.21082-6-leo.yan@linaro.org


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