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

Kernel low-level debugging messages via Tegra UART B

configname: CONFIG_TEGRA_DEBUG_UARTB

Kernel low-level debugging port
└─>Kernel low-level debugging messages via Tegra UART B
In linux kernel since version 2.6.36 (release Date: 2010-10-20)  
Say Y here if you want kernel low-level debugging support
on Tegra based platforms.