perf tools: Add fake_pmu to parse_group() function

perf tools: Add fake_pmu to parse_group() function

Allow to pass fake_pmu in parse_groups function so it can be used in
parse_events call.

It's will be passed by the upcoming metricgroup__parse_groups_test
function.

Committer notes:

Made it a 'struct perf_pmu' pointer, in line with the changes at the
start of this patchkit to avoid statics deep down in library code.

Acked-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200602214741.1218986-6-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>