CONFIG_SOC_IMX31 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_SOC_IMX31 (not configurable)

modulename: mm-imx3.ko

and/or

clk-imx31.ko

configname: CONFIG_SOC_IMX31

Linux Kernel Configuration
└─>Freescale i.MX support
└─>SOC_IMX31
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
source code:
/arch/arm/mach-imx/