iommu/vt-d: Remove domain_alloc_paging()

This is duplicated by intel_iommu_domain_alloc_paging_flags(), just remove
it.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Link: https://lore.kernel.org/r/0-v1-b101d00c5ee5+17645-vtd_paging_flags_jgg@nvidia.com


Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>