CONFIG_SCB0_MI1_SLOT21 is not available for thedefaultarchitecture x86.
Result is shown for architecture blackfin
default or selected kernelversion does not have config value CONFIG_SCB0_MI1_SLOT21.
Result is shown for kernelversion 6.7-rc3

Slot 21 slave interface id

configname: CONFIG_SCB0_MI1_SLOT21

Linux Kernel Configuration
└─>BF609 Specific Configuration
└─>SCB0 Master Interface 1 (SMC)
└─>Slot 21 slave interface id
In linux kernel since version 3.12 (release Date: 2013-11-03)