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

CONFIG_PPC_OF_PLATFORM_PCI (not configurable)

configname: CONFIG_PPC_OF_PLATFORM_PCI

Linux/PowerPC Kernel Configuration
└─>Processor support
└─>PPC_OF_PLATFORM_PCI
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
depends
CONFIG_PPC64 or CONFIG_PCI or &