sony-laptop: adjust keyboard backlight values for off/auto/on

Keyboard backlight can be always off, use some automatic trigger
(activity and light sensor), always on.
The behaviour of the driver changes whereby previously when passed 1 it
tried to turn on backlight immediately now it does nothing. This is
however a bug fix since (a) it makes little sense to turn on the
backlight when control is automatic and (b) this behaviour is
consistent with what the windows driver does.

Signed-off-by: Javier Achirica <jachirica@gmail.com>
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>