AMD IOMMU: set iommu for device from ACPI code too

The device<->iommu relationship has to be set from the information in the ACPI
table too. This patch adds this logic to the driver.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: iommu@lists.linux-foundation.org
Cc: bhavna.sarathy@amd.com
Cc: robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>