ACPI: PM: Set s2idle_wakeup earlier and clear it later

The role of the s2idle_wakeup variable is to cause
acpi_pm_wakeup_event() and acpi_pm_notify_handler() to
increment pm_abort_suspend and trigger a wakeup from
suspend-to-idle in case the ACPI SCI wakeup was canceled
by acpi_s2idle_wake().

However, for this purpose it need not be set in acpi_s2idle_wake()
and cleared in acpi_s2idle_sync(), respectively.  In fact, it
may be set as early as in acpi_s2idle_prepare() and cleared as
late as in acpi_s2idle_restore(), so do that to allow subsequent
changes to be simpler.

This change is not expected to alter functionality.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>