default or selected kernelversion does not have config value CONFIG_SERIAL_S3C2400.
Result is shown for kernelversion 5.6.18

Samsung S3C2410 Serial port support

modulename: s3c2400.ko

configname: CONFIG_SERIAL_S3C2400

Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>Serial drivers
└─>Samsung S3C2410 Serial port support
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
Serial port support for the Samsung S3C2400 SoC

source code:
drivers/tty/serial/s3c2400.c