samsung-laptop: put all local variables in a single structure

Even if this driver can only be loaded once, it is still a good
idea to create some kind of context structure.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Matthew Garrett <mjg@redhat.com>