iommu/arm-smmu-v3: Add support for domain_alloc_user fn

iommu/arm-smmu-v3: Add support for domain_alloc_user fn

This will be used by iommufd for allocating usr managed domains and is
also required when we add support for iommufd based dirty tracking
support.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Link: https://lore.kernel.org/r/20240703101604.2576-2-shameerali.kolothum.thodi@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>