classmate-laptop: Use struct dev_pm_ops for power management

Make the classmate-laptop driver define its PM callbacks through
a struct dev_pm_ops object rather than by using legacy PM hooks
in struct acpi_device_ops.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>