CONFIG_ARCH_AT91SAM9G20 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

AT91SAM9G20

modulename: at91sam9260.ko

and/or

at91sam9260_devices.ko

configname: CONFIG_ARCH_AT91SAM9G20

Atmel AT91 Processor
└─>AT91SAM9G20
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
source code:
/arch/arm/mach-at91/

is selected by
CONFIG_MACB