Revert "try 2 core min"
This reverts commit bd6e1fdad782f4a1890ec61531a0e904618c9331.
...because I've got a better idea! See next commit...
Following 'try 2 core minimum' - this time with sleep

The previous commit prevented the device from entering deep sleep.
I've put a flag in the hotplugging code that keeps track of
whether the device is asleep or awake. I'm using that to inhibit
the two core minimum if the device is asleep. Seems to have fixed
the issue.

A two core minimum allows the frequency governor to rest at 192MHz
as intended. Previously, on one core, the device kept jumping up to
702MHz. If I understand the power comsumption of a processor
correctly, 702MHz will use 3.5 times the power of 192MHz. Of course
I now have two cores active. I assume that this is probably
slightly less than double the power requirement of 192MHz on one
core alone, due to some global overheads of having the chip awake.
Unless I'm mistaken, having the second core always online should
provide a power saving in this configuration. It will at the very
least prevent some spurious hotplugging.