CONFIG_S3C_ADC is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

ADC common driver support

modulename: dev-adc.ko

and/or

adc.ko

configname: CONFIG_S3C_ADC

Linux Kernel Configuration
└─>ADC common driver support
In linux kernel since version 2.6.34 (release Date: 2010-05-16)  
Core support for the ADC block found in the Samsung SoC systems
for drivers such as the touchscreen and hwmon to use to share
this resource.

source code:
depends
CONFIG_PLAT_SAMSUNG |
| CONFIG_SAMSUNG_ATAGS or  NOT CONFIG_ARCH_MULTIPLATFORM