x86, AMD IOMMU: initialize dma_ops from IOMMU initialization and enable IOMMUs

This patch adds a call to the driver specific dma_ops initialization routine
from the AMD IOMMU hardware initialization. Further it adds the necessary code
to finally enable AMD IOMMU hardware.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: iommu@lists.linux-foundation.org
Cc: bhavna.sarathy@amd.com
Cc: Sebastian.Biemueller@amd.com
Cc: robert.richter@amd.com
Cc: joro@8bytes.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>