CONFIG_PLAT_S5P is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_PLAT_S5P (not configurable)

configname: CONFIG_PLAT_S5P

Linux Kernel Configuration
└─>PLAT_S5P
In linux kernel since version 2.6.34 (release Date: 2010-05-16)  
Base platform code for Samsung's S5P series SoC.