ARM: dts: sunxi: Enable PWM controller on Q8 format tablets

Q8 format tablets use channel 0 of the PWM controller for backlight dimming.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>