Suspend: Fix compilation warning for CONFIG_SUSPEND unset

Suspend: Make debug facility depend on CONFIG_SUSPEND

Make the new suspend debug facility code depend on CONFIG_SUSPEND,
as appropriate, to remove the compiler warning printed when CONFIG_PM is set
and CONFIG_SUSPEND is not set.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Len Brown <len.brown@intel.com>