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
└─>DEBUG_UART_8250
In linux kernel since version 3.10 (release Date: 2013-06-30)  
is depended by
CONFIG_DEBUG_ALPINE_UART0
CONFIG_DEBUG_BCM_5301X
CONFIG_DEBUG_BCM_HR2
CONFIG_DEBUG_BCM_IPROC_UART3
CONFIG_DEBUG_BCM_KONA_UART
CONFIG_DEBUG_BERLIN_UART
CONFIG_DEBUG_DAVINCI_DA8XX_UART1
CONFIG_DEBUG_DAVINCI_DA8XX_UART2
CONFIG_DEBUG_FOOTBRIDGE_COM1
CONFIG_DEBUG_GEMINI
CONFIG_DEBUG_HIP01_UART
CONFIG_DEBUG_HIP04_UART
CONFIG_DEBUG_KEYSTONE_UART0
CONFIG_DEBUG_KEYSTONE_UART1
CONFIG_DEBUG_LPC18XX_UART0
CONFIG_DEBUG_LPC32XX
CONFIG_DEBUG_MMP_UART2
CONFIG_DEBUG_MMP_UART3
CONFIG_DEBUG_MVEBU_UART0
CONFIG_DEBUG_MVEBU_UART0_ALTERNATE
CONFIG_DEBUG_MVEBU_UART1_ALTERNATE
CONFIG_DEBUG_MSTARV7_PMUART
CONFIG_DEBUG_MT6589_UART0
CONFIG_DEBUG_MT8127_UART0
CONFIG_DEBUG_MT8135_UART3
CONFIG_DEBUG_NSPIRE_CLASSIC_UART
CONFIG_DEBUG_OMAP1UART1
CONFIG_DEBUG_OMAP1UART2
CONFIG_DEBUG_OMAP1UART3
CONFIG_DEBUG_OMAP2UART1
CONFIG_DEBUG_OMAP2UART2
CONFIG_DEBUG_OMAP2UART3
CONFIG_DEBUG_OMAP3UART3
CONFIG_DEBUG_OMAP4UART3
CONFIG_DEBUG_OMAP3UART4
CONFIG_DEBUG_OMAP4UART4
CONFIG_DEBUG_TI81XXUART1
CONFIG_DEBUG_TI81XXUART2
CONFIG_DEBUG_TI81XXUART3
CONFIG_DEBUG_AM33XXUART1
CONFIG_DEBUG_PXA_UART1
CONFIG_DEBUG_RV1108_UART0
CONFIG_DEBUG_RV1108_UART1
CONFIG_DEBUG_RV1108_UART2
CONFIG_DEBUG_RK29_UART0
CONFIG_DEBUG_RK29_UART1
CONFIG_DEBUG_RK29_UART2
CONFIG_DEBUG_RK3X_UART0
CONFIG_DEBUG_RK3X_UART1
CONFIG_DEBUG_RK3X_UART2
CONFIG_DEBUG_RK3X_UART3
CONFIG_DEBUG_RK32_UART2
CONFIG_DEBUG_SD5203_UART
CONFIG_DEBUG_SOCFPGA_UART0
CONFIG_DEBUG_SOCFPGA_ARRIA10_UART1
CONFIG_DEBUG_SOCFPGA_CYCLONE5_UART1
CONFIG_DEBUG_SUN9I_UART0
CONFIG_DEBUG_SUNXI_UART0
CONFIG_DEBUG_SUNXI_UART1
CONFIG_DEBUG_SUNXI_R_UART