CONFIG_MACH_PXA3XX_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support PXA3xx platforms from device tree

modulename: pxa-dt.ko

configname: CONFIG_MACH_PXA3XX_DT

Linux Kernel Configuration
└─>Intel PXA2xx/PXA3xx Implementations
└─>Support PXA3xx platforms from device tree
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Include support for Marvell PXA3xx based platforms using
the device tree. Needn't select any other machine while
MACH_PXA3XX_DT is enabled.

source code: