iommu/amd: Remove domain_alloc()

iommu/amd: Remove domain_alloc()

IOMMU drivers should not be sensitive to the domain type, a paging domain
should be created based only on the flags passed in, the same for all
callers.

AMD was using the domain_alloc() path to force VFIO into a v1 domain type,
because v1 gives higher performance. However now that
IOMMU_HWPT_ALLOC_PASID is present, and a NULL device is not possible,
domain_alloc_paging_flags() will do the right thing for VFIO.

When invoked from VFIO flags will be 0 and the amd_iommu_pgtable type of
domain will be selected. This is v1 by default unless the kernel command
line has overridden it to v2.

If the admin is forcing v2 assume they know what they are doing so force
it everywhere, including for VFIO.

Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/2-v2-9776c53c2966+1c7-amd_paging_flags_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>