CONFIG_MACH_AT91SAM9G20EK_2MMC is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Atmel AT91SAM9G20-EK Evaluation Kit with 2 SD/MMC Slots

configname: CONFIG_MACH_AT91SAM9G20EK_2MMC

Linux Kernel Configuration
└─>Atmel AT91 System-on-Chip
└─>Atmel AT91SAM9G20-EK Evaluation Kit with 2 SD/MMC Slots
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
Select this if you are using an Atmel AT91SAM9G20-EK Evaluation Kit
with 2 SD/MMC Slots. This is the case for AT91SAM9G20-EK rev. C and
onwards.