CONFIG_HAVE_AT91_DBGU1 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_HAVE_AT91_DBGU1 (not configurable)

configname: CONFIG_HAVE_AT91_DBGU1

Linux Kernel Configuration
└─>HAVE_AT91_DBGU1
In linux kernel since version 3.1 (release Date: 2011-10-24)  

is depended by
CONFIG_SOC_SAMA5D3