Enable Intel IOMMU scalable mode by default


Linux Kernel Configuration
└─>Device Drivers
└─>IOMMU Hardware Support
└─>Enable Intel IOMMU scalable mode by default
In linux kernel since version 5.1 (release Date: 2019-05-05)  
Selecting this option will enable by default the scalable mode if
hardware presents the capability. The scalable mode is defined in
VT-d 3.0. The scalable mode capability could be checked by reading
/sys/devices/virtual/iommu/dmar*/intel-iommu/ecap. If this option
is not selected, scalable mode support could also be enabled by
passing intel_iommu=sm_on to the kernel. If not sure, please use
the default value.