iommu/arm-smmu-v3: Clean up address masking

Before trying to add the SMMUv3.1 support for 52-bit addresses, make
things bearable by cleaning up the various address mask definitions to
use GENMASK_ULL() consistently. The fact that doing so reveals (and
fixes) a latent off-by-one in Q_BASE_ADDR_MASK only goes to show what a
jolly good idea it is...

Tested-by: Nate Watterson <nwatters@codeaurora.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>