backlight: add minimum backlight brightness module param.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: flar2 <asegaert@gmail.com>
backlight: scale max current when the brightness level is below 15 instead of using always 0.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: flar2 <asegaert@gmail.com>
modules
Linear 2.7