CONFIG_MACH_NET5BIG_V2 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

LaCie 5Big Network v2 NAS Board

modulename: netxbig_v2-setup.ko

configname: CONFIG_MACH_NET5BIG_V2

Linux Kernel Configuration
└─>Marvell Kirkwood Implementations
└─>LaCie 5Big Network v2 NAS Board
In linux kernel since version 2.6.35 (release Date: 2010-08-01)  
Say 'Y' here if you want your kernel to support the
LaCie 5Big Network v2 NAS.

source code:
/arch/arm/mach-kirkwood/