Revert "hrtimer: Prevent enqueue of hrtimer on dead CPU"

This reverts commit e805ced7efd8961499932a5d5b73803e23709e2f.
Revert "hrtimer: Consider preemption when migrating hrtimer cpu_bases"

This reverts commit a68e83b425628656ee2fd8ba460f06598039ab81.
Revert "board-8974: enable ram console"

This reverts commit dfced63217934a70c6df1d23459d7f72e6cfb30a.
Revert "sched: reinitialize rq->next_balance when a CPU is hot-added"

This reverts commit 267b11317c27f3d1f0c5193e5803875173716ea4.