CONFIG_ARCH_IXP2000 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

IXP2400/2800-based

modulename: uengine.ko

configname: CONFIG_ARCH_IXP2000

ARM system type
└─>IXP2400/2800-based
In linux kernel since version 2.6.12  
Support for Intel's IXP2400/2800 (XScale) family of processors.

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

depends
CONFIG_MMU

is selected by
CONFIG_I2C_IXP2000