Revert "ARM: SMP: use a timing out completion for cpu hotplug"

Now we decided to use previous hotplug timer.

Thanks nomanman for testing.

This reverts commit d41c723eb8fc7608d8ec2b3989199df8aa398f05.
defconfig: version tag 7.0 -> 7.2
Revert "ARM: disable preemption in machine_shutdown"

This reverts commit 17f43074e008fa8755a733cb19ca2eaf5616d385.

This will cause BUGS on cfs scheduler when machine is shutting down.