hw/i386: Introduce AMD IOMMU

Add AMD IOMMU emulaton to Qemu in addition to Intel IOMMU.
The IOMMU does basic translation, error checking and has a
minimal IOTLB implementation. This IOMMU bypassed the need
for target aborts by responding with IOMMU_NONE access rights
and exempts the region 0xfee00000-0xfeefffff from translation
as it is the q35 interrupt region.

We advertise features that are not yet implemented to please
the Linux IOMMU driver.

IOTLB aims at implementing commands on real IOMMUs which is
essential for debugging and may not offer any performance
benefits

Signed-off-by: David Kiarie <davidkiarie4@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>