CONFIG_MACH_KIRKWOOD is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Marvell Kirkwood boards


Linux Kernel Configuration
└─>Marvell Engineering Business Unit (MVEBU) SoCs
└─>Marvell Kirkwood boards
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Say 'Y' here if you want your kernel to support boards based
on the Marvell Kirkwood device tree.