CONFIG_CPU_MIPSR6 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_CPU_MIPSR6 (not configurable)

configname: CONFIG_CPU_MIPSR6

Linux Kernel Configuration
└─>CPU_MIPSR6
In linux kernel since version 3.10 (release Date: 2013-06-30)