CONFIG_AT91_DEBUG_LL_DBGU0 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
Kernel low-level debugging on rm9200, 9260/9g20, 9261/9g10 and 9rl
configname: CONFIG_AT91_DEBUG_LL_DBGU0
Kernel low-level debugging port
└─>Kernel low-level debugging on rm9200, 9260/9g20, 9261/9g10 and 9rl