CONFIG_DEBUG_MMP_UART3 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Kernel low-level debugging message via MMP UART3

configname: CONFIG_DEBUG_MMP_UART3

Kernel low-level debugging port
└─>Kernel low-level debugging message via MMP UART3
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Say Y here if you want kernel low-level debugging support
on MMP UART3.