platform/chrome: chromeos_laptop: make chromeos_laptop const

Declare chromeos_laptop structures as const as they are only used during
a copy operation. As their value is never modified during runtime, they
can be made const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Benson Leung <bleung@chromium.org>