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

Support for the ARM Power State Coordination Interface (PSCI)

modulename: psci.ko

configname: CONFIG_ARM_PSCI

Linux Kernel Configuration
└─>Kernel Features
└─>Support for the ARM Power State Coordination Interface (PSCI)
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Say Y here if you want Linux to communicate with system firmware
implementing the PSCI specification for CPU-centric power
management operations described in ARM document number ARM DEN
0022A ("Power State Coordination Interface System Software on
ARM processors").

source code: