perf pmu: Make pmu_add_sys_aliases() public

perf pmu: Make pmu_add_sys_aliases() public

Function pmu_add_sys_aliases() will be required for the PMU events test
for system events aliases, so make it public.

Signed-off-by: John Garry <john.garry@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jin Yao <yao.jin@linux.intel.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>
Cc: linuxarm@huawei.com
Link: https //lore.kernel.org/r/1627566986-30605-10-git-send-email-john.garry@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>