iommu/vt-d: Remove intel_iommu::domains

The "domains" field of the intel_iommu structure keeps the mapping of
domain_id to dmar_domain. This information is not used anywhere. Remove
and cleanup it to avoid unnecessary memory consumption.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20220214025704.3184654-1-baolu.lu@linux.intel.com
Link: https://lore.kernel.org/r/20220301020159.633356-2-baolu.lu@linux.intel.com


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