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

PXA2xx/PXA3xx-based

configname: CONFIG_ARCH_PXA

ARM system type
└─>PXA2xx/PXA3xx-based
In linux kernel since version 2.6.12  
Support for Intel/Marvell's PXA2xx/PXA3xx processor line.