CONFIG_SOC_AT91RM9200 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
AT91RM9200
modulename: at91rm9200.ko
configname: CONFIG_SOC_AT91RM9200
Linux Kernel Configuration
└─>AT91/Microchip SoCs
└─>AT91RM9200
In linux kernel since version 3.1 (release Date: 2011-10-24)
Select this if you are using Microchip's AT91RM9200 SoC.