CONFIG_POWER4 is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_POWER4 (not configurable)

configname: CONFIG_POWER4

Linux Kernel Configuration
└─>Processor support
└─>POWER4
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  

is selected by
CONFIG_PPC_PMAC64