CONFIG_SOC_AT91SAM9X5 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

AT91SAM9x5 family

modulename: at91sam9x5.ko

configname: CONFIG_SOC_AT91SAM9X5

Linux Kernel Configuration
└─>Atmel AT91 System-on-Chip
└─>AT91SAM9x5 family
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Select this if you are using one of Atmel's AT91SAM9x5 family SoC.
This means that your SAM9 name finishes with a '5' (except if it is
AT91SAM9G45!).
This support covers AT91SAM9G15, AT91SAM9G25, AT91SAM9X25, AT91SAM9G35
and AT91SAM9X35.

source code: