CONFIG_CPU_R4X00 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

R4x00

modulename: c-r4k.ko

and/or

dump_tlb.ko

and/or

r4k_fpu.ko

configname: CONFIG_CPU_R4X00

CPU type
└─>R4x00
In linux kernel since version 2.6.12  
MIPS Technologies R4000-series processors other than 4300, including
the R4000, R4400, R4600, and 4700.

source code:
arch/mips/mm/