CONFIG_PPC_BOOK3S is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_PPC_BOOK3S (not configurable)

configname: CONFIG_PPC_BOOK3S

Linux Kernel Configuration
└─>Processor support
└─>PPC_BOOK3S
In linux kernel since version 2.6.30 (release Date: 2009-06-09)  
depends
CONFIG_6xx or CONFIG_PPC64

is selected by
CONFIG_6xx