These values can be computed from the other values already stored in the
config. Move the calculation to arm_smmu_write_strtab() and do it directly
before writing the registers.

This moves all the logic to calculate the two registers into one function
from three and saves an unimportant 16 bytes from the arm_smmu_device.
Suggested-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/4-v4-6416877274e1+1af-smmuv3_tidy_jgg@nvidia.comSigned-off-by: Will Deacon <will@kernel.org>