CONFIG_BUILTIN_DTB_SOURCE is not available for thedefaultarchitecture x86.
Result is shown for architecture sh

Source file for builtin DTB

configname: CONFIG_BUILTIN_DTB_SOURCE

Linux Kernel Configuration
└─>Boot options
└─>Source file for builtin DTB
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Base name (without suffix, relative to arch/sh/boot/dts) for the
a DTS file that will be used to produce the DTB linked into the
kernel.