sony-laptop: use soft rfkill status stored in hw

The SNC device on recent Vaio laptops also stores the soft status and
leaves it available after reboot. Use it and always set the last soft
and hard status on module load.

[malattia@linux.it: patch taken from a largely modified sony-laptop.c,
smaller modifications to the original code to simplify it]

Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Matthew Garrett <mjg@redhat.com>