The hooks were populated but the power down left the CPU in limbo-land.
What we need to do - until there is a way to actually power off - is to
turn off the MMU and enter the spinning loop as if we were cold-booted.
This allows the on-call to pick up the CPU again.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Change-Id: Iefc7a58424e3578ad3dd355a7bd6eaba4b412699