[$] Power-efficient workqueues

Power-efficient workqueues were first introduced in the 3.11 kernel release; since then, fifty or sosubsystems and drivers have been updated to use them. These workqueuescan be especially useful on handheld devices (like tablets andsmartphones), where power is at a premium.ARM platforms with power-efficient workqueues enabled on Ubuntu andAndroid have shown significant improvements in energy consumption (up to15% for some use cases).