CONFIG_CPU_PXA26x is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_CPU_PXA26x (not configurable)

configname: CONFIG_CPU_PXA26x

Linux Kernel Configuration
└─>CPU_PXA26x
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
Select code specific to PXA26x (codename Dalhart)

selects
CONFIG_PXA25x

depends
CONFIG_ARCH_PXA

is depended by
CONFIG_MACH_HIMALAYA