[PATCH v2 7/7] i440fx: add an iommu

Don't laugh so loudly, that's an attempt at a variant of Shannon's perfect cipher after all. Hey, not everyone can afford an infinite key length!
Okay, while we are on savings, we could equivalently save the XOR step and not do any enc^D^D^D scrambling at all for an even cheaper, faster and nearly as (un)secure variant...