classmate-laptop: Add support for Classmate V4 accelerometer.

Classmate V4 laptop includes a new accelerometer that can't be handled by
previous driver. This patch adds a new driver to handle it.

[mjg: Fixed up the driver pm stuff]
Signed-off-by: Miguel Gómez <magomez@igalia.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>