CONFIG_DEBUG_MT8135_UART3 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Mediatek mt8135 UART3

configname: CONFIG_DEBUG_MT8135_UART3

Kernel low-level debugging port
└─>Mediatek mt8135 UART3
In linux kernel since version 3.19 (release Date: 2015-02-08)  
Say Y here if you want kernel low-level debugging support
for Mediatek mt8135 based platforms on UART3.