CONFIG_SOC_AM43XX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

TI AM43x

modulename: prm33xx.ko

configname: CONFIG_SOC_AM43XX

Linux Kernel Configuration
└─>TI AM43x
In linux kernel since version 3.10 (release Date: 2013-06-30)  
source code:
/arch/arm/mach-omap2/