CONFIG_SWIOTLB is not available for thedefaultarchitecture x86.
Result is shown for architecture ia64

CONFIG_SWIOTLB (not configurable)

modulename: swiotlb.ko

and/or

pci-swiotlb.ko

configname: CONFIG_SWIOTLB

IA-64 Linux Kernel Configuration
└─>Processor type and features
└─>SWIOTLB
In linux kernel since version 2.6.12  
source code:
lib/swiotlb.c