sony-laptop: keyboard backlight fixes

Restore the original state on module removal, set the latest values on
resume.
When setting the keyboard backlight mode try to turn on/off backlight
immediately.

[malattia@linux.it: patch taken from a largely modified sony-laptop.c,
ported and slightly modified to use defines already available.]

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