intel-iommu: introduce Intel IOMMU (VT-d) emulation

Add support for emulating Intel IOMMU according to the VT-d specification for
the q35 chipset machine. Implement the logics for DMAR (DMA remapping) without
PASID support. The emulation supports register-based invalidation and primary
fault logging.

Signed-off-by: Le Tan <tamlokveer@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
