CONFIG_CPU_MIPSR2_IRQ_EI is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_CPU_MIPSR2_IRQ_EI (not configurable)

configname: CONFIG_CPU_MIPSR2_IRQ_EI

Linux Kernel Configuration
└─>Kernel type
└─>CPU_MIPSR2_IRQ_EI
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
is depended by
CONFIG_MIPS_MT_SMP