perf evsel: Separate missing feature detection from evsel__open_cpu()

perf evsel: Separate missing feature detection from evsel__open_cpu()

This is a preparatory patch for the workqueue patches with the goal to
separate in evlist__open_cpu() the actual opening, which could be
performed in parallel, from the existing fallback mechanisms, which
should be handled sequentially.

This patch separates the missing feature detection in evsel__open_cpu()
into a new evsel__detect_missing_features() function.

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/cba0b7d939862473662adeedb0f9c9b69566ee9a.1629490974.git.rickyman7@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>