CONFIG_DEBUG_SPEAR13XX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Kernel low-level debugging messages via ST SPEAr 13xx UART

configname: CONFIG_DEBUG_SPEAR13XX

Kernel low-level debugging port
└─>Kernel low-level debugging messages via ST SPEAr 13xx UART
In linux kernel since version 4.1 (release Date: 2015-06-21)  
Say Y here if you want kernel low-level debugging support
on ST SPEAr13xx based platforms.