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

STMicroelectronics Consumer Electronics SOCs

modulename: board-dt.ko

configname: CONFIG_ARCH_STI

Linux Kernel Configuration
└─>STMicroelectronics Consumer Electronics SOCs
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Include support for STMicroelectronics' STiH415/416, STiH407/10 and
STiH418 family SoCs using the Device Tree for discovery. More
information can be found in Documentation/arm/sti/ and
source code:
arch/arm/mach-sti/board-dt.c


is selected by
CONFIG_DRM_STI