CONFIG_DEBUG_MVEBU_UART0_ALTERNATE is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

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

configname: CONFIG_DEBUG_MVEBU_UART0_ALTERNATE

Kernel low-level debugging port
└─>Kernel low-level debugging messages via MVEBU UART0 (new 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 new bootloaders
that remap the internal registers at 0xf1000000.

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.