CONFIG_MACH_AT91RM9200EK is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Atmel AT91RM9200-EK Evaluation Kit

modulename: board-ek.ko

and/or

board-rm9200ek.ko

configname: CONFIG_MACH_AT91RM9200EK

Linux Kernel Configuration
└─>AT91RM9200 Implementations
└─>Atmel AT91RM9200-EK Evaluation Kit
In linux kernel since version 2.6.16 (release Date: 2006-03-19)  
Select this if you are using Atmel's AT91RM9200-EK Evaluation Kit

source code:
arch/arm/mach-at91rm9200/board-ek.c