CONFIG_MACH_STM32F769 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

STMicroelectronics STM32F769

configname: CONFIG_MACH_STM32F769

Linux Kernel Configuration
└─>STMicroelectronics STM32 family
└─>STMicroelectronics STM32F769
In linux kernel since version 4.2 (release Date: 2015-08-30)  

is selected by
CONFIG_STM32F7_DEBUG_UART