AMD K8 and newer will trap when enabling the NX support outside PAE
paging mode. The AMD64 wake code was restoring the MSR EFER to switch to
Long Mode and naturally didn't have paging enabled at that point.
While this works fine with Intel CPUs, it resulted in an immediate
reboot with AMD processors.
Fixed by a joint brain storming session of jmcneill@, cegger@ and
myself, based on some input from the hardware developers. This fixes
PR 38587.
ACPI wakeup code and teach it how to start the APs again. As a side
effect the CPU_START interface allows choosing between different
bootstrap codes more easily now.
