CONFIG_ARC_PLAT_SIM is not available for thedefaultarchitecture x86.
Result is shown for architecture arc
default or selected kernelversion does not have config value CONFIG_ARC_PLAT_SIM.
Result is shown for kernelversion 6.4.14

ARC nSIM based simulation virtual platforms

configname: CONFIG_ARC_PLAT_SIM

Linux Kernel Configuration
└─>ARC nSIM based simulation virtual platforms
In linux kernel since version 4.1 (release Date: 2015-06-21)  
Support for nSIM based ARC simulation platforms
This includes the standalone nSIM (uart only) vs. System C OSCI VP