MAINTAINERS: Add entry for perf tool arm64 pmu-events files

MAINTAINERS: Add entry for perf tool arm64 pmu-events files

Will and I have an interest in reviewing the pmu-events changes related
to arm64, so add a specific entry for this.

Signed-off-by: John Garry <john.garry@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: linuxarm@huawei.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: Will Deacon <will@kernel.org>
Link: http://lore.kernel.org/lkml/1570611273-108281-1-git-send-email-john.garry@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>