CONFIG_MACH_SMDK6450 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
SMDK6450
modulename: mach-smdk6450.ko
configname: CONFIG_MACH_SMDK6450
Linux Kernel Configuration
└─>SMDK6450
In linux kernel since version 2.6.37 (release Date: 2011-01-04)
Machine support for the Samsung SMDK6450