iommu/vt-d: Remove has_iotlb_device flag

iommu/vt-d: Remove has_iotlb_device flag

The has_iotlb_device flag was used to indicate if a domain had attached
devices with ATS enabled. Domains without this flag didn't require device
TLB invalidation during unmap operations, optimizing performance by
avoiding unnecessary device iteration.

With the introduction of cache tags, this flag is no longer needed. The
code to iterate over attached devices was removed by commit 06792d067989
("iommu/vt-d: Cleanup use of iommu_flush_iotlb_psi()").

Remove has_iotlb_device to avoid unnecessary code.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240809055431.36513-5-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>