CONFIG_UDBG_RTAS_CONSOLE is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

RTAS based debug console

configname: CONFIG_UDBG_RTAS_CONSOLE

Linux/PowerPC Kernel Configuration
└─>Platform support
└─>RTAS based debug console
In linux kernel since version 2.6.18 (release Date: 2006-09-19)