CONFIG_DEBUG_IMX50_UART is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

i.MX50 Debug UART

configname: CONFIG_DEBUG_IMX50_UART

Kernel low-level debugging port
└─>i.MX50 Debug UART
In linux kernel since version 3.14 (release Date: 2014-03-30)  
Say Y here if you want kernel low-level debugging support
on i.MX50.