CONFIG_FIT_IMAGE_FDT_OCELOT_PCB123 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips
default or selected kernelversion does not have config value CONFIG_FIT_IMAGE_FDT_OCELOT_PCB123.
Result is shown for kernelversion 6.8.9

Include FDT for Microsemi Ocelot PCB123

configname: CONFIG_FIT_IMAGE_FDT_OCELOT_PCB123

Linux Kernel Configuration
└─>Include FDT for Microsemi Ocelot PCB123
In linux kernel since version 4.2 (release Date: 2015-08-30)  
Enable this to include the FDT for the Ocelot PCB123 platform
from Microsemi in the FIT kernel image.
This requires u-boot on the platform.