iommu/amd: Add domain_alloc_user based domain allocation

Add the domain_alloc_user op implementation. To that end, refactor
amd_iommu_domain_alloc() to receive a dev pointer and flags, while renaming
it too, such that it becomes a common function shared with
domain_alloc_user() implementation. The sole difference with
domain_alloc_user() is that we initialize also other fields that
iommu_domain_alloc() does. It lets it return the iommu domain correctly
initialized in one function.

This is in preparation to add dirty enforcement on AMD implementation of
domain_alloc_user.

Link: https://lore.kernel.org/r/20231024135109.73787-11-joao.m.martins@oracle.com


Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>