per-device dma_map_ops for intel-iommu?

[Christoph Hellwig]

Hi David and Joerg,

do you remember a good reason why intel-iommu is not using per-device
dma_map_ops like the AMD iommu or the various ARM iommus?

Right now intel-iommu.c contains a half-asses reimplementation of the
dma direct code for the iommu_no_mapping() case, and it would seem
much nicer to just fall back to that case and not even call into
intel-iommu in that case.