iommu/arm-smmu-v3: Introduce struct arm_smmu_event

Introduce `struct arm_smmu_event` to represent event records.
Parse out relevant fields from raw event records for ease and
use the new `struct arm_smmu_event` instead.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
Link: https://lore.kernel.org/r/20241203184906.2264528-2-praan@google.com


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