CONFIG_TEGRA_DEBUG_UARTB is not available for the selected architecture x86.
Result is shown for architecture arm

UART-B

configname: CONFIG_TEGRA_DEBUG_UARTB

Low-level debug console UART
└─>UART-B
In linux kernel since version 2.6.36 (release Date: 2010-10-20)
selects
CONFIG_DEBUG_TEGRA_UART

depends
 or CONFIG_ARCH_TEGRA