VT-d: suppress UR signaling for desktop chipsets

VT-d: suppress UR signaling for desktop chipsets

Unsupported Requests can be signaled for malformed writes to the MSI
address region, e.g. due to buggy or malicious DMA set up to that
region. These should normally result in IOMMU faults, but don't on
the desktop chipsets dealt with here.

This is CVE-2013-3495 / XSA-59.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Don Dugger <donald.d.dugger@intel.com>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Xiantao Zhang <xiantao.zhang@intel.com>