platform/chrome: cros_ec_lpc: wake up from s2idle on Chrome EC

Chrome platform installed a Chrome EC notify handler which prevents
default EC GPE handler getting called. Add pm_system_wakeup to the
Chrome EC notify handler so wake up from s2idle can happen.

Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Wenkai Du <wenkai.du@intel.com>
Signed-off-by: Benson Leung <bleung@chromium.org>