CONFIG_MACH_NETXBIG is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_MACH_NETXBIG.
Result is shown for kernelversion 5.4.229

LaCie 2Big and 5Big Network v2

modulename: netxbig.ko

configname: CONFIG_MACH_NETXBIG

Linux Kernel Configuration
└─>Marvell Engineering Business Unit (MVEBU) SoCs
└─>LaCie 2Big and 5Big Network v2
In linux kernel since version 3.17 (release Date: 2014-10-05)  
Say 'Y' here if you want your kernel to support the
LaCie 2Big and 5Big Network v2

source code:
arch/arm/mach-mvebu/netxbig.c