CONFIG_PLAT_S3C64XX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_PLAT_S3C64XX (not configurable)

configname: CONFIG_PLAT_S3C64XX

Linux Kernel Configuration
└─>PLAT_S3C64XX
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
Base platform code for any Samsung S3C64XX device

selects
CONFIG_PM_GENERIC_DOMAINS
CONFIG_SAMSUNG_WAKEMASK


is selected by
CONFIG_VIDEO_S3C_CAMIF