iommu/vt-d: Refactor iommu information of each domain

iommu/vt-d: Refactor iommu information of each domain

When a DMA domain is attached to a device, it needs to allocate a domain
ID from its IOMMU. Currently, the domain ID information is stored in two
static arrays embedded in the domain structure. This can lead to memory
waste when the driver is running on a small platform.

This optimizes these static arrays by replacing them with an xarray and
consuming memory on demand.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Steve Wahl <steve.wahl@hpe.com>
Link: https://lore.kernel.org/r/20220702015610.2849494-4-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>