iommu/arm-smmu-v3: Move the STE generation for S1 and S2 domains into functions

This is preparation to move the STE calculation higher up in to the call
chain and remove arm_smmu_write_strtab_ent(). These new functions will be
called directly from attach_dev.

Reviewed-by: Moritz Fischer <mdf@kernel.org>
Reviewed-by: Michael Shavit <mshavit@google.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Moritz Fischer <moritzf@google.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/3-v6-96275f25c39d+2d4-smmuv3_newapi_p1_jgg@nvidia.com


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