CONFIG_405_CPU is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc
default or selected kernelversion does not have config value CONFIG_405_CPU.
Result is shown for kernelversion 6.9.9

40x family

configname: CONFIG_405_CPU

CPU selection
└─>40x family
In linux kernel since version 6 (release Date: 2022-10-02)  
depends
CONFIG_40x
NOT CONFIG_CC_IS_CLANG