iommu/arm-smmu-v3: Clean up queue definitions

As with registers and tables, use GENMASK and the bitfield accessors
consistently for queue fields, to save some lines and ease maintenance
a little. This now leaves everything in a nice state where all named
field definitions expect to be used with bitfield accessors (although
since single-bit fields can still be used directly we leave some of
those uses as-is to avoid unnecessary churn), while the few remaining
*_MASK definitions apply exclusively to in-place values.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>