CONFIG_MACH_PXA25X_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support PXA25x platforms from device tree

modulename: pxa-dt.ko

configname: CONFIG_MACH_PXA25X_DT

Linux Kernel Configuration
└─>Intel PXA2xx/PXA3xx Implementations
└─>Support PXA25x platforms from device tree
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Include support for Marvell PXA25x based platforms using
the device tree. Needn't select any other machine while
MACH_PXA25x_DT is enabled.

source code: