CONFIG_CPU_PXA320 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_CPU_PXA320 (not configurable)

modulename: pxa320.ko

configname: CONFIG_CPU_PXA320

Linux Kernel Configuration
└─>CPU_PXA320
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
PXA320 (codename Monahans-P)

source code:
selects
CONFIG_PXA3xx

depends
CONFIG_ARCH_PXA

is depended by
CONFIG_MACH_PXA3XX_DT