CONFIG_ARCH_IXP23XX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_IXP23XX.
Result is shown for kernelversion 6.2.5

IXP23XX-based

modulename: uengine.ko

configname: CONFIG_ARCH_IXP23XX

ARM system type
└─>IXP23XX-based
In linux kernel since version 2.6.17 (release Date: 2006-06-17)  
Support for Intel's IXP23xx (XScale) family of processors.

source code:
arch/arm/common/uengine.c

depends
CONFIG_MMU