default or selected kernelversion does not have config value CONFIG_NET_BFIN.
Result is shown for kernelversion 6.6.1

Blackfin devices

configname: CONFIG_NET_BFIN

Linux Kernel Configuration
└─> Device Drivers
└─> Network device support
└─> Ethernet driver support
└─> Blackfin devices

In linux kernel since version 3.1 (release Date: 2011-10-24)  

If you have a network (Ethernet) card belonging to this class, say Y.

If unsure, say Y.

Note that the answer to this question doesn't directly affect the
kernel: saying N will just cause the configurator to skip all
the remaining Blackfin card questions. If you say Y, you will be
asked for your specific card in the following questions.