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

IXP2400/2800-based

configname: CONFIG_ARCH_IXP2000

ARM system type
└─>IXP2400/2800-based
In linux kernel since version 2.6.12  
selects
CONFIG_PCI

is selected by
CONFIG_CPU_XSCALE