CONFIG_AT91_DEBUG_LL_DBGU1 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Kernel low-level debugging on 9263, 9g45 and sama5d3

configname: CONFIG_AT91_DEBUG_LL_DBGU1

Kernel low-level debugging port
└─>Kernel low-level debugging on 9263, 9g45 and sama5d3
In linux kernel since version 3.1 (release Date: 2011-10-24)