acpidump IVRS table format: change 'IOMMUId' into 'IOMMU DeviceId'

and apply the consistent format for device ids used in other IVRS
elements. The field seems to be the PCI Device ID of the IOMMU itself,
instead of an abstract unit ID.

Sponsored by: Advanced Micro Devices (AMD)
Sponsored by: The FreeBSD Foundation
MFC after: 1 week