AMD,IOMMU: Clean up old entries in remapping tables when creating new one

AMD,IOMMU: Clean up old entries in remapping tables when creating new one

When changing the affinity of an IRQ associated with a passed
through PCI device, clear previous mapping.

This is XSA-36 / CVE-2013-0153.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
In addition, because some BIOSes may incorrectly program IVRS
entries for IOAPIC try to check for entry's consistency. Specifically,
if conflicting entries are found disable IOMMU if per-device
remapping table is used. If entries refer to bogus IOAPIC IDs
disable IOMMU unconditionally

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@amd.com>
xen-unstable changeset: 26517:601139e2b0db
xen-unstable date: Tue Feb  5 14:20:47 UTC 2013