CONFIG_OMAP_IOMMU is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_OMAP_IOMMU (not configurable)

modulename: iommu2.ko

and/or

iommu.ko

configname: CONFIG_OMAP_IOMMU

Linux Kernel Configuration
└─>TI OMAP Common Features
└─>OMAP_IOMMU
In linux kernel since version 2.6.31 (release Date: 2009-09-09)  
source code:
arch/arm/mach-omap2/iommu2.c

is depended by
CONFIG_VIDEO_OMAP3