Add a basic set of data points which count the number of sleep entries
that are being done by the OS.

For now this'll match up with the "wakeups"; although I'll dig deeper into
this to see if we can determine which sleep state the CPU managed to get
into. Most things I've seen these days only expose up to C2 or C3 via
ACPI even though the CPU goes all the way down to C6 or C7.