CONFIG_BOARD_SPEAR600_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
SPEAr600 generic board configured via device-tree
configname: CONFIG_BOARD_SPEAR600_DT
Linux Kernel Configuration
└─>SPEAr6xx Implementations
└─>SPEAr600 generic board configured via device-tree
In linux kernel since version 3.4 (release Date: 2012-05-20)
Supports ST SPEAr600 boards configured via the device-tree