Add support for deep(er) idle states that can be entered using PSCI. For

Add support for deep(er) idle states that can be entered using PSCI.  For
now this only supports states advertised in device trees, but ACPI support
could be added as well.  The parsing of the idle states as well as the
heuristic to pick the deepest one is probably a bit to simple, but more
complex cases can be added later.  Worst case cores will use WFI and use
more power in suspend.

ok phessler@