msi-laptop: Use struct dev_pm_ops for power management

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

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Lee, Chun-Yi <jlee@suse.com>