CONFIG_ARCH_DAVINCI_DM646x is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

DaVinci 646x based system

modulename: dm646x.ko

configname: CONFIG_ARCH_DAVINCI_DM646x

Linux Kernel Configuration
└─>TI DaVinci Implementations
└─>DaVinci 646x based system
In linux kernel since version 2.6.31 (release Date: 2009-09-09)  
source code:
/arch/arm/mach-davinci/