CONFIG_SOC_IMX25 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_SOC_IMX25 (not configurable)

modulename: cpu-imx25.ko

and/or

clk-imx25.ko

configname: CONFIG_SOC_IMX25

Linux Kernel Configuration
└─>Freescale i.MX support
└─>SOC_IMX25
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
source code:
/arch/arm/mach-imx/