CONFIG_ARCH_AT91SAM9261 is not available for the selected architecture x86.
Result is shown for architecture arm

AT91SAM9261

modulename: at91sam9261.ko

and/or

at91sam9261_devices.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/
selects
CONFIG_SOC_AT91SAM9261
CONFIG_AT91_USE_OLD_CLK
CONFIG_OLD_IRQ_AT91

is selected by
CONFIG_CPU_ARM926T