drm/sun4i: Add R40 display engine compatible

R40 has versatile display pipeline. It supports two simultanious outputs
on various outputs (TVE, VGA, HDMI, MIPI DSI, LCD).

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>
Link: https://patchwork.freedesktop.org/patch/msgid/20180710203511.18454-3-jernej.skrabec@siol.net