CONFIG_ARCH_AT91SAM9261 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

AT91SAM9261

modulename: at91sam9261.ko

configname: CONFIG_ARCH_AT91SAM9261

Atmel AT91 Processor
└─>AT91SAM9261
In linux kernel since version 2.6.18 (release Date: 2006-09-19)  
source code:
/arch/arm/mach-at91/