CONFIG_MACH_SMDK2412 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

SMDK2412

configname: CONFIG_MACH_SMDK2412

Linux Kernel Configuration
└─>S3C2412 Machines
└─>SMDK2412
In linux kernel since version 2.6.22 (release Date: 2007-07-08)  
Say Y here if you are using an SMDK2412

Note, this shares support with SMDK2413, so will automatically
select MACH_SMDK2413.