CONFIG_ARCH_STM32 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
STMicroelectronics STM32 family
configname: CONFIG_ARCH_STM32
Linux Kernel Configuration
└─>STMicroelectronics STM32 family
In linux kernel since version 3.10 (release Date: 2013-06-30)
Support for STMicroelectronics STM32 processors.