CONFIG_NDS32_BUILTIN_DTB is not available for thedefaultarchitecture x86.
Result is shown for architecture nds32

Builtin DTB

configname: CONFIG_NDS32_BUILTIN_DTB

Linux Kernel Configuration
└─>System Type
└─>Builtin DTB
In linux kernel since version 4.2 (release Date: 2015-08-30)  
User can use it to specify the dts of the SoC