CONFIG_4xx_SOC is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_4xx_SOC (not configurable)

modulename: ppc4xx_soc.ko

and/or

soc.ko

configname: CONFIG_4xx_SOC

Linux/PowerPC Kernel Configuration
└─>Bus options
└─>4xx_SOC
In linux kernel since version 2.6.26 (release Date: 2008-07-13)  
source code:
arch/powerpc/sysdev/ppc4xx_soc.c