CONFIG_PLAT_S3C is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_PLAT_S3C (not configurable)

configname: CONFIG_PLAT_S3C

Linux Kernel Configuration
└─>PLAT_S3C
In linux kernel since version 2.6.23 (release Date: 2007-10-09)  
Base platform code for any Samsung S3C device


depends
CONFIG_ARCH_S3C2410 or CONFIG_ARCH_S3C24A0 or CONFIG_ARCH_S3C64XX

is selected by
CONFIG_SERIAL_SAMSUNG

is depended by
CONFIG_PLAT_S3C64XX