ARM: dts: sun8i: r40: Remove fallback display engine compatible

R40 has pretty unique display pipeline. Because of that, H3 display
engine compatible fallback should be removed.

Fixes: 05a43a26 ("ARM: dts: sun8i: r40: Add HDMI pipeline")

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>