CONFIG_X86_IO_APIC (not configurable)

modulename: io_apic.ko

configname: CONFIG_X86_IO_APIC

Linux Kernel Configuration for x86
└─>Processor type and features
└─>X86_IO_APIC
In linux kernel since version 2.6.12  
source code:
arch/x86/kernel/apic/io_apic.c

is selected by
CONFIG_IRQ_REMAP