CONFIG_ARCH_KIRKWOOD_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_KIRKWOOD_DT.
Result is shown for kernelversion 6.5.1

Marvell Kirkwood Flattened Device Tree

modulename: board-dt.ko

configname: CONFIG_ARCH_KIRKWOOD_DT

Linux Kernel Configuration
└─>Marvell Kirkwood Implementations
└─>Marvell Kirkwood Flattened Device Tree
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Say 'Y' here if you want your kernel to support the
Marvell Kirkwood using flattened device tree.

source code:
arch/arm/mach-kirkwood/board-dt.c