CONFIG_ARCH_BITMAIN is not available for the selected architecture x86.
Result is shown for architecture arm64
Bitmain SoC Platforms
configname: CONFIG_ARCH_BITMAIN
Linux Kernel Configuration
└─>Platform selection
└─>Bitmain SoC Platforms
In linux kernel since version 5.1 (release Date: 2019-05-05)
This enables support for the Bitmain SoC Family.