ACPI: PM: s2idle: Eliminate acpi_sleep_no_ec_events()

Change acpi_ec_suspend() to use pm_suspend_no_platform() instead of
acpi_sleep_no_ec_events(), which allows the latter to be eliminated
along with the s2idle_in_progress variable which is only used by it.

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