CONFIG_AT91_EARLY_DBGU0 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_AT91_EARLY_DBGU0.
Result is shown for kernelversion 5.3.7

DBGU on rm9200, 9260/9g20, 9261/9g10 and 9rl

configname: CONFIG_AT91_EARLY_DBGU0

Select a UART for early kernel messages
└─>DBGU on rm9200, 9260/9g20, 9261/9g10 and 9rl
In linux kernel since version 3.3 (release Date: 2012-03-18)