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: NCorentin Chary <corentincj@iksaif.net>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: NMatthew Garrett <mjg@redhat.com>