AMD IOMMU: allow command line overrides for broken IVRS tables

AMD IOMMU: allow command line overrides for broken IVRS tables

With there being so many systems with broken ACPI tables, and with it
generally being known what's wrong with those tables, give people a
handle to overcome the resulting disabling of their IOMMUs.

Inspired by Linux side patches providing similar functionality.

Suggested-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-By: Sander Eikelenboom <linux@eikelenboom.it>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: Suravee Suthikulpanit <suravee.suthikulapanit@amd.com>