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

CONFIG_PPC_ICS_RTAS (not configurable)

modulename: ics-rtas.ko

configname: CONFIG_PPC_ICS_RTAS

Linux Kernel Configuration
└─>PPC_ICS_RTAS
In linux kernel since version 3 (release Date: 2011-07-21)  
source code:
arch/powerpc/sysdev/xics/ics-rtas.c
is depended by
CONFIG_PPC_POWERNV_RTAS