Revert "hotplug: restructuring data structures"

This reverts commit 7fd0e701a1676d05260e287a506d9c3825be12ce.
hotplug: delay initial workqueue start

By delaying it a bit, we workaround some kind of
race condition. Enabling effectively four cores
during boot might be a good idea anyway.

Signed-off-by: Blechd0se <alex.christ@hotmail.de>
hotplug: fix core 4 would eventually not go down

We only check if our current cpu is online, not thinking about
which position it might be currently. This would result in a very
long uptime for the fourth cpu even when there is zero load.

The solution is actually pretty simple; we just check every case
and offline accordingly to that. Also reducing the overhead of the
driver a bit and cleaning up unneeded stuff.

Signed-off-by: Blechd0se <alex.christ@hotmail.de>