CONFIG_MACH_SMDK6440 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
SMDK6440
modulename: mach-smdk6440.ko
configname: CONFIG_MACH_SMDK6440
Linux Kernel Configuration
└─>SMDK6440
In linux kernel since version 2.6.34 (release Date: 2010-05-16)
Machine support for the Samsung SMDK6440