tegra_hotplug: speed up suspend/resume code

 * merged with @franciscofranco additions regarding
   the suspend/resume logic. They are now in their
   own dedicated workqueue

 * Furthermore do some cleanup and coding style fixes

Signed-off-by: Blechd0se <alex.christ@hotmail.de>
hotplug: switch to singlethread_workqueue()

When we create a workqueue we should consider that
it also creates kernel threads. Before this patch
we would have a dedicated workqueue for each
processor on the system. This patch reduces the overhead
and only creates a single workqueue.

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