CONFIG_ZONE_DMA32 is not available for the selected architecture x86.
Result is shown for architecture ia64

CONFIG_ZONE_DMA32 (not configurable)

configname: CONFIG_ZONE_DMA32

Linux Kernel Configuration
└─>Processor type and features
└─>ZONE_DMA32
In linux kernel since version 2.6.19 (release Date: 2006-11-29)