ACPI: PM: Loop in full LPS0 mode only

After a previous change, all non-wakeup GPEs are disabled for
suspend-to-idle unless full Low-Power S0 (LPS0) mode is in use, so
it is not necessary to do anything in acpi_s2idle_wake() unless in
full LPS0 mode, which is only when lps0_device_handle is set.

Modify the code accordingly.

Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>