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

CONFIG_CPU_BMIPS (not configurable)

modulename: smp-bmips.ko

configname: CONFIG_CPU_BMIPS

Linux Kernel Configuration
└─>CPU selection
└─>CPU_BMIPS
In linux kernel since version 3.1 (release Date: 2011-10-24)  
source code:
arch/mips/kernel/

depends
 or CONFIG_SYS_HAS_CPU_BMIPS