CONFIG_SYS_SUPPORTS_ZBOOT_UART16550 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips
CONFIG_SYS_SUPPORTS_ZBOOT_UART16550 (not configurable)
configname: CONFIG_SYS_SUPPORTS_ZBOOT_UART16550
Linux/MIPS Kernel Configuration
└─>CPU selection
└─>SYS_SUPPORTS_ZBOOT_UART16550