Add a way to create a pmu event without the actual PMU being in place.

This way we can test metrics defined for any processor.

The interface is to define fake_pmu in struct parse_events_state data.
It will be used only in tests via special interface function added in
following changes.
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Acked-by: NIan Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200602214741.1218986-2-jolsa@kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>