CONFIG_PLAT_S5PC1XX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_PLAT_S5PC1XX (not configurable)

configname: CONFIG_PLAT_S5PC1XX

Linux Kernel Configuration
└─>PLAT_S5PC1XX
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
Base platform code for any Samsung S5PC1XX device