CONFIG_ARCH_AT91SAM9X5 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_AT91SAM9X5.
Result is shown for kernelversion 5.3.7

AT91SAM9x5 family

modulename: at91sam9x5.ko

configname: CONFIG_ARCH_AT91SAM9X5

Atmel AT91 Processor
└─>AT91SAM9x5 family
In linux kernel since version 3.4 (release Date: 2012-05-20)  
source code:
/arch/arm/mach-at91/