CONFIG_DEBUG_IMX25_UART is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

i.MX25 Debug UART

configname: CONFIG_DEBUG_IMX25_UART

Kernel low-level debugging port
└─>i.MX25 Debug UART
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Say Y here if you want kernel low-level debugging support
on i.MX25.