CONFIG_SOC_SAMA5 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_SOC_SAMA5 (not configurable)

modulename: sama5.ko

configname: CONFIG_SOC_SAMA5

Linux Kernel Configuration
└─>AT91/Microchip SoCs
└─>SOC_SAMA5
In linux kernel since version 3.1 (release Date: 2011-10-24)  
source code:
arch/arm/mach-at91/sama5.c