platform/chrome: chromeos_laptop - Use deferred probing

Further refactor chromeos_laptop, adding a probe function.
Init will call dmi_check_system, but will only use the match to select
a chromeos_laptop structure of the current board.

Probe will add the devices, and on errors return -EPROBE_DEFER.
If i2c adapters are loaded after chromeos_laptop inits, the deferred
probe will instantiate the peripherals when the bus appears.

Signed-off-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Signed-off-by: Olof Johansson <olof@lixom.net>