CONFIG_CPU_PXA310 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_CPU_PXA310 (not configurable)

configname: CONFIG_CPU_PXA310

Linux Kernel Configuration
└─>PXA2xx/PXA3xx-based
└─>CPU_PXA310
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
PXA310 (codename Monahans-LV)