drivers/perf: Simplify the SMMUv3 PMU event attributes

For each PMU event, there is a SMMU_EVENT_ATTR(xx, XX) and
&smmu_event_attr_xx.attr.attr. Let's redefine the SMMU_EVENT_ATTR
to simplify the smmu_pmu_events.

Signed-off-by: Qi Liu <liuqi115@huawei.com>
Link: https://lore.kernel.org/r/1612789498-12957-1-git-send-email-liuqi115@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>