CONFIG_SOC_STIH407 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

STiH407 STMicroelectronics Consumer Electronics family

configname: CONFIG_SOC_STIH407

Linux Kernel Configuration
└─>STMicroelectronics Consumer Electronics SOCs
└─>STiH407 STMicroelectronics Consumer Electronics family
In linux kernel since version 3.19 (release Date: 2015-02-08)  
This enables support for STMicroelectronics Digital Consumer
Electronics family StiH407 parts, targetted at set-top-box
and other digital audio/video applications using Flattened Device
Trees.