CONFIG_MACH_RD88F5182_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Marvell Orion-NAS Reference Design (Flattened Device Tree)

modulename: board-rd88f5182.ko

configname: CONFIG_MACH_RD88F5182_DT

Linux Kernel Configuration
└─>Marvell Orion
└─>Marvell Orion-NAS Reference Design (Flattened Device Tree)
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Say 'Y' here if you want your kernel to support the Marvell
Orion-NAS (88F5182) RD2, Flattened Device Tree.

source code:
/arch/arm/mach-orion5x/board-rd88f5182.c