CONFIG_DEBUG_MVEBU_UART0 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Kernel low-level debugging messages via MVEBU UART0 (old bootloaders)


Kernel low-level debugging port
└─>Kernel low-level debugging messages via MVEBU UART0 (old bootloaders)
In linux kernel since version 4 (release Date: 2015-04-12)  
Say Y here if you want kernel low-level debugging support
on MVEBU based platforms on UART0.

This option should be used with the old bootloaders
that left the internal registers mapped at
0xd0000000. As of today, this is the case on
platforms such as the Globalscale Mirabox or the
Plathome OpenBlocks AX3, when using the original

This option will not work on older Marvell platforms
(Kirkwood, Dove, MV78xx0, Orion5x), which should pick
the "new bootloader" variant.

If the wrong DEBUG_MVEBU_UART* option is selected,
when u-boot hands over to the kernel, the system
silently crashes, with no serial output at all.