kernelconfig_penguin
selects
CONFIG_CPU_IDLE

depends
CONFIG_ACPI

is depended by
CONFIG_ACPI_PROCESSOR

CONFIG_ACPI_PROCESSOR_IDLE (not configurable)

configname: CONFIG_ACPI_PROCESSOR_IDLE

Linux Kernel Configuration
└─> Power management and ACPI options
└─> ACPI (Advanced Configuration and Power Interface) Support
└─> ACPI_PROCESSOR_IDLE