CONFIG_DMA_COHERENT is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_DMA_COHERENT (not configurable)

modulename: dma-coherent.ko

configname: CONFIG_DMA_COHERENT

Linux/MIPS Kernel Configuration
└─>Machine selection
└─>DMA_COHERENT
In linux kernel since version 2.6.12  
source code:
arch/mips/mm/dma-coherent.c