drm/rockchip: Use iommu_paging_domain_alloc()

Commit <421be3ee> ("drm/rockchip: Refactor IOMMU initialisation") has
refactored rockchip_drm_init_iommu() to pass a device that the domain is
allocated for. Replace iommu_domain_alloc() with
iommu_paging_domain_alloc() to retire the former.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Andy Yan <andyshrk@163.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240902014700.66095-3-baolu.lu@linux.intel.com