drm/sun4i: Add compatible for the A10s pipeline

The A10s has a slightly different display pipeline than the A13, with an
HDMI controller.

Add a compatible for it.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>