CONFIG_EP405 is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc
default or selected kernelversion does not have config value CONFIG_EP405.
Result is shown for kernelversion 6.9.9

EP405/EP405PC

modulename: ep405.ko

configname: CONFIG_EP405

Linux Kernel Configuration
└─>EP405/EP405PC
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
This option enables support for the EP405/EP405PC boards.

source code:
arch/powerpc/platforms/40x/ep405.c

depends
CONFIG_40x