CONFIG_40x is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

AMCC 40x

modulename: 40x_mmu.ko

configname: CONFIG_40x

Processor Type
└─>AMCC 40x
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
source code:
arch/powerpc/mm/40x_mmu.c