CONFIG_IA64_DIG_VTD is not available for thedefaultarchitecture x86.
Result is shown for architecture ia64
default or selected kernelversion does not have config value CONFIG_IA64_DIG_VTD.
Result is shown for kernelversion 6.9.5

DIG+Intel+IOMMU

configname: CONFIG_IA64_DIG_VTD

System type
└─>DIG+Intel+IOMMU
In linux kernel since version 2.6.28 (release Date: 2008-12-24)  
selects
CONFIG_INTEL_IOMMU
CONFIG_PCI_MSI