CONFIG_DEBUG_S3C64XX_UART is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_DEBUG_S3C64XX_UART (not configurable)

configname: CONFIG_DEBUG_S3C64XX_UART

Linux Kernel Configuration
└─>DEBUG_S3C64XX_UART
In linux kernel since version 4.1 (release Date: 2015-06-21)