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

i.MX Debug UART Port Selection

configname: CONFIG_DEBUG_IMX_UART_PORT

Linux Kernel Configuration
└─>i.MX Debug UART Port Selection
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Choose UART port on which kernel low-level debug messages
should be output.