iommu/amd: Initialize dma_ops for hotplug and sriov devices

When a device is added to the system at runtime the AMD
IOMMU driver initializes the necessary data structures to
handle translation for it. But it forgets to change the
per-device dma_ops to point to the AMD IOMMU driver. So
mapping actually never happens and all DMA accesses end in
an IO_PAGE_FAULT. Fix this.

Reported-by: Stefan Assmann <sassmann@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>