iommu/vt-d: Cleanup si_domain

The static identity domain has been introduced, rendering the si_domain
obsolete. Remove si_domain and cleanup the code accordingly.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240809055431.36513-8-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>