CONFIG_ARCH_BAST is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_BAST.
Result is shown for kernelversion 6.9.9

Simtec Electronics BAST (EB2410ITX)

modulename: mach-bast.ko

configname: CONFIG_ARCH_BAST

Linux Kernel Configuration
└─>Samsung S3C24XX SoCs (deprecated, see help)
└─>Samsung S3C24XX SoCs Support
└─>Simtec Electronics BAST (EB2410ITX)
In linux kernel since version 2.6.12  
Say Y here if you are using the Simtec Electronics EB2410ITX
development board (also known as BAST)