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

Broadcom BMIPS

modulename: smp-bmips.ko

configname: CONFIG_CPU_BMIPS

CPU type
└─>Broadcom BMIPS
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Support for BMIPS32/3300/4350/4380 and BMIPS5000 processors.

source code:
arch/mips/kernel/