CONFIG_DEBUG_UART_BCM63XX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_DEBUG_UART_BCM63XX.
Result is shown for kernelversion 5.4.229

CONFIG_DEBUG_UART_BCM63XX (not configurable)

configname: CONFIG_DEBUG_UART_BCM63XX

Linux Kernel Configuration
└─>Kernel hacking
└─>DEBUG_UART_BCM63XX
In linux kernel since version 3.18 (release Date: 2014-12-07)  
is depended by
CONFIG_DEBUG_BCM63XX