platform/chrome: chromeos_laptop - discard data for unneeded boards

Mark board data as __intconst/__initdata and make a copy of appropriate
entry once we identified the board we are running on. The rest of the data
will be discarded once the kernel finished booting (or module finished
loading).

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Benson Leung <bleung@chromium.org>