ARM: dts: sun8i: Add touchscreen node for sun8i-a23-polaroid-mid2809pxe04

Add a node enabling the gsl3670 touchscreen controller found on
sun8i-a23-polaroid-mid2809pxe04 tablets.

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