CONFIG_DEBUG_VEXPRESS_UART0_CA9 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Use PL011 UART0 at 0x10009000 (V2P-CA9 core tile)

configname: CONFIG_DEBUG_VEXPRESS_UART0_CA9

Kernel low-level debugging port
└─>Use PL011 UART0 at 0x10009000 (V2P-CA9 core tile)
In linux kernel since version 3.1 (release Date: 2011-10-24)  
This option selects UART0 at 0x10009000. Except for custom models,
this applies only to the V2P-CA9 tile.