iommu/amd: Add support for IOMMU XT mode

The AMD IOMMU XT mode enables interrupt remapping with 32-bit destination
APIC ID, which is required for x2APIC. The feature is available when
the XTSup bit is set in the IOMMU Extended Feature register
and/or the IVHD Type 10h IOMMU Feature Reporting field.

For more information, please see section "IOMMU x2APIC Support" of
the AMD I/O Virtualization Technology (IOMMU) Specification.

Cc: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>