Commit "rcu: Create RCU-specific workqueues with rescuers" switched RCU
to using local workqueses and removed power efficiency flag from them.
This caused a performance regression that can be observed in Geekbench 5
after enabling CONFIG_WQ_POWER_EFFICIENT_DEFAULT: score went down from
760/2500 to 620/2300 (single/multi core respectively).
Add WQ_POWER_EFFICIENT flag to avoid this regression.
Change-Id: I2c4f41faa55548f9e81a1c0cbe10703948062d89