Host event can be sent by remoteproc by any time, and
cros_ec_rpmsg_callback would be called after cros_ec_rpmsg_create_ept.
But the cros_ec_device is initialized after that, which cause host event
handler to use cros_ec_device that are not initialized properly yet.

Fix this by don't schedule host event handler before cros_ec_register
returns. Instead, remember that we have a pending host event, and
schedule host event handler after cros_ec_register.

Fixes: 71cddb70 ("platform/chrome: cros_ec_rpmsg: Fix race with host command when probe failed.")
Signed-off-by: NPi-Hsun Shih <pihsun@chromium.org>
Signed-off-by: NEnric Balletbo i Serra <enric.balletbo@collabora.com>