CONFIG_S3C64XX_DEV_SPI is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_S3C64XX_DEV_SPI (not configurable)

modulename: dev-spi.ko

configname: CONFIG_S3C64XX_DEV_SPI

Linux Kernel Configuration
└─>S3C64XX_DEV_SPI
In linux kernel since version 2.6.34 (release Date: 2010-05-16)  
Compile in platform device definitions for S3C64XX's type
SPI controllers.

source code:

is depended by
CONFIG_MACH_SMDK6450