ARM: dts: sun8i: Add backlight / pwm nodes to sun8i-a23-gt90h-v4

Add nodes for the backlight / pwm found on a23-gt90h-v4 tablets.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>