CONFIG_PXA3xx is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_PXA3xx (not configurable)

modulename: cpufreq-pxa3xx.ko

and/or

mfp-pxa3xx.ko

configname: CONFIG_PXA3xx

Linux Kernel Configuration
└─>PXA3xx
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
Select code specific to PXA3xx variants

source code:
arch/arm/mach-pxa/cpufreq-pxa3xx.c
selects
CONFIG_CPU_XSC3

depends
CONFIG_ARCH_PXA