it83xx: implement reboot wait-ext

This was missed on it83xx, but is helpful for servod
to work reliably. Refactor save_flags to use common code.

BUG=b:77830536
TEST=(not yet done) it waits 10 sec for external reboot.

Change-Id: Ia2aac1879d73ac11dd7f3dfc13a1dd871905473e
Signed-off-by: Nick Sanders <nsanders@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1018597
Tested-by: Dino Li <Dino.Li@ite.com.tw>
Reviewed-by: Jett Rink <jettrink@chromium.org>
1 file changed