amd-iommu: add flush iommu_ops

amd-iommu: add flush iommu_ops

The iommu_ops structure contains two methods for flushing: 'iotlb_flush' and
'iotlb_flush_all'. This patch adds implementations of these for AMD IOMMUs.

The iotlb_flush method takes a base DFN and a (4k) page count, but the
flush needs to be done by page order (i.e. 0, 9 or 18). Because a flush
operation is fairly expensive to perform, the code calculates the minimum
order single flush that will cover the specified page range rather than
performing multiple flushes.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Brian Woods <brian.woods@amd.com>