Revert "kthread_work: wake up worker only when the worker is idle"

This reverts commit 9b66f2809c14c33ee495cb18bfb58fd47604aac5.
Revert "Hotplug thread infrastructure"

This reverts commit a287a197c308111b7ff939f9088c353fdb476f54.
Revert "Revert "Squash 'enhance power efficiency' patches""

This reverts commit 1d89bc2b16a2308152c7a97b46f69fe644822e0f.