CONFIG_SYS_HAS_CPU_MIPS64_R5 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_SYS_HAS_CPU_MIPS64_R5 (not configurable)

configname: CONFIG_SYS_HAS_CPU_MIPS64_R5

Linux Kernel Configuration
└─>CPU selection
└─>SYS_HAS_CPU_MIPS64_R5
In linux kernel since version 5.2 (release Date: 2019-07-07)  
is selected by
CONFIG_CPU_MIPS64_R5