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

Support MXS platforms from device tree

modulename: mach-mxs.ko

configname: CONFIG_MACH_MXS_DT

Linux Kernel Configuration
└─>Support MXS platforms from device tree
In linux kernel since version 3.5 (release Date: 2012-07-21)  
Include support for Freescale MXS platforms(i.MX23 and i.MX28)
using the device tree for discovery

source code: