ACPI: PM: s2idle: Switch EC over to polling during "noirq" suspend

Since the ACPI SCI is set up for system wakeup before the "noirq"
suspend of devices, it is better to make suspend-to-idle follow
suspend-to-RAM (S3) and switch over the EC to polling during "noirq"
suspend (and back to interrupt-based flow during "noirq" resume).

The frequency of spurious wakeup interrupts from the EC may be
reduced this way.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>