CONFIG_DEBUG_UART_8250 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_DEBUG_UART_8250 (not configurable)

configname: CONFIG_DEBUG_UART_8250

Linux Kernel Configuration
└─>Kernel hacking
└─>DEBUG_UART_8250
In linux kernel since version 3.10 (release Date: 2013-06-30)