Change API of acpiiort(4). It was written as a hook before, taking the

Change API of acpiiort(4).  It was written as a hook before, taking the
PCI attach args and replacing the DMA tag inside.  Our other IOMMU API
though takes a DMA tag and returns the old one or a new one.  To have
acpiiort(4) integrate better with non-PCI ACPI devices, change the API
so that it is more similar to the other API.  This also makes the code
easier to understand.

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