CONFIG_PXA25x is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_PXA25x (not configurable)

modulename: cpufreq-pxa2xx.ko

and/or

mfp-pxa2xx.ko

configname: CONFIG_PXA25x

Linux Kernel Configuration
└─>PXA25x
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Select code specific to PXA21x/25x/26x variants

source code:
arch/arm/mach-pxa/cpufreq-pxa2xx.c

depends
CONFIG_ARCH_PXA

is selected by
CONFIG_USB_PXA25X

is depended by
CONFIG_ARCH_LUBBOCK