CONFIG_MACH_NETSPACE_V2_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

LaCie Network Space v2 NAS (Flattened Device Tree)

modulename: board-ns2.ko

configname: CONFIG_MACH_NETSPACE_V2_DT

Linux Kernel Configuration
└─>Marvell Kirkwood Implementations
└─>LaCie Network Space v2 NAS (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 LaCie
Network Space v2 NAS, using Flattened Device Tree.

source code:
arch/arm/mach-kirkwood/board-ns2.c