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

NETGEAR ReadyNAS Duo v2 (Flattened Device Tree)

modulename: board-readynas.ko

configname: CONFIG_MACH_READYNAS_DT

Linux Kernel Configuration
└─>Marvell Kirkwood Implementations
└─>NETGEAR ReadyNAS Duo v2 (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
NETGEAR ReadyNAS Duo v2 using Fattened Device Tree.

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