iommu/arm-smmu-v3: Expose the arm_smmu_attach interface

iommu/arm-smmu-v3: Expose the arm_smmu_attach interface

The arm-smmuv3-iommufd.c file will need to call these functions too.
Remove statics and put them in the header file. Remove the kunit
visibility protections from arm_smmu_make_abort_ste() and
arm_smmu_make_s2_domain_ste().

Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Donald Dutile <ddutile@redhat.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/7-v4-9e99b76f3518+3a8-smmuv3_nesting_jgg@nvidia.com
Signed-off-by: Will Deacon <will@kernel.org>