CONFIG_IBMEBUS is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

Support for GX bus based adapters

modulename: ibmebus.ko

configname: CONFIG_IBMEBUS

Linux/PowerPC Kernel Configuration
└─>Platform support
└─>Support for GX bus based adapters
In linux kernel since version 2.6.16 (release Date: 2006-03-19)  
Bus device driver for GX bus based adapters.

source code:
arch/powerpc/kernel/ibmebus.c