ol the keyboard backlight.

SLKB and GLKB are used to get/set the backlight. On
the U50VG is supports 4 brightness level, but this may
change with other models.

SLKB take a 8 bit integer where the higher bit is used
to toggle the backlight, and the over 7 bits control the
brightness level.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Len Brown <len.brown@intel.com>
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