CONFIG_CPU_BMIPS5000 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_CPU_BMIPS5000 (not configurable)

configname: CONFIG_CPU_BMIPS5000

Linux Kernel Configuration
└─>CPU selection
└─>CPU_BMIPS5000
In linux kernel since version 2.6.37 (release Date: 2011-01-04)