CONFIG_SOC_AR5312 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Atheros AR5312/AR2312+ SoC support

modulename: ar5312.ko

configname: CONFIG_SOC_AR5312

Linux Kernel Configuration
└─>Atheros AR5312/AR2312+ SoC support
In linux kernel since version 3.10 (release Date: 2013-06-30)  
source code:
arch/mips/ath25/ar5312.c
depends
CONFIG_ATH25