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

Proc interface to RTAS

modulename: rtas-proc.ko

configname: CONFIG_RTAS_PROC

Linux/PowerPC Kernel Configuration
└─>Platform support
└─>Proc interface to RTAS
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
source code:
arch/powerpc/kernel/rtas-proc.c

is depended by
CONFIG_PPC_EFIKA