gpu: host1x: Use iommu_paging_domain_alloc()

An iommu domain is allocated in host1x_iommu_attach() and is attached to
host->dev. Use iommu_paging_domain_alloc() to make it explicit.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20240610085555.88197-8-baolu.lu@linux.intel.com


Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240812071605.9513-1-baolu.lu@linux.intel.com