CONFIG_MACH_S3C64XX_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Samsung S3C6400/S3C6410 machine using Device Tree

configname: CONFIG_MACH_S3C64XX_DT

Linux Kernel Configuration
└─>Samsung S3C64XX
└─>Samsung S3C6400/S3C6410 machine using Device Tree
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Machine support for Samsung S3C6400/S3C6410 machines with Device Tree
enabled.
Select this if a fdt blob is available for your S3C64XX SoC based
board.
Note: This is under development and not all peripherals can be
supported with this machine file.