drivers: video: Add backlight dimmer option

This is based on n5dim by @mzhou  https://github.com/mzhou/n5dim

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
drivers: video: gradual transitions for backlight dimmer

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
video: backlight: enable backlight_dimmer by default. Auto-brightness looks great with this.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>