platform/chrome: cros_ec_rpmsg: Add host command AP sleep state support

Add EC host command to inform EC of AP suspend/resume status.

Signed-off-by: Yilun Lin <yllin@chromium.org>
Tested-by: Pi-Hsun Shih <pihsun@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>