CONFIG_BFIN_IDLE_LED_NUM is not available for thedefaultarchitecture x86.
Result is shown for architecture blackfin
default or selected kernelversion does not have config value CONFIG_BFIN_IDLE_LED_NUM.
Result is shown for kernelversion 5.13-rc2

LED

configname: CONFIG_BFIN_IDLE_LED_NUM

Blackfin Kernel Configuration
└─>Blackfin Processor Options
└─>Board customizations
└─>LED
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
Select the LED (marked on the board) for you to blink.