CONFIG_IRQ_CPU_RM9K is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_IRQ_CPU_RM9K (not configurable)

modulename: irq-rm9000.ko

configname: CONFIG_IRQ_CPU_RM9K

Linux Kernel Configuration
└─>IRQ_CPU_RM9K
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
source code:
arch/mips/kernel/irq-rm9000.c