CONFIG_ARCH_AT91 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_AT91.
Result is shown for kernelversion 6.9.9

AT91/Microchip SoCs

configname: CONFIG_ARCH_AT91

Linux Kernel Configuration
└─>AT91/Microchip SoCs
In linux kernel since version 2.6.18 (release Date: 2006-09-19)