iommu/arm-smmu-v3: Rename arm_smmu_master_data to arm_smmu_master

The arm_smmu_master_data structure already represents more than just the
firmware data associated to a master, and will be used extensively to
represent a device's state when implementing more SMMU features. Rename
the structure to arm_smmu_master.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>