CONFIG_ARCH_AT91SAM9G45 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

AT91SAM9G45

modulename: at91sam9g45.ko

configname: CONFIG_ARCH_AT91SAM9G45

Atmel AT91 Processor
└─>AT91SAM9G45
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
source code:
/arch/arm/mach-at91/

is selected by
CONFIG_USB_ATMEL_USBA