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

Radix MMU Support

modulename: pgtable-radix.ko

and/or

hugetlbpage-radix.ko

configname: CONFIG_PPC_RADIX_MMU

Linux Kernel Configuration
└─>Processor support
└─>Radix MMU Support
In linux kernel since version 4.1 (release Date: 2015-06-21)  
Enable support for the Power ISA 3.0 Radix style MMU. Currently this
is only implemented by IBM Power9 CPUs, if you don't have one of them
you can probably disable this.

source code:
arch/powerpc/mm/