drm/sun4i: Add support for H6 DE3 mixer 0

Mixer 0 has 1 VI and 3 UI planes, scaler on all planes and can output
4K image @60Hz. It also support 10 bit colors, which are not yet
implemented.

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/20181104182705.18047-14-jernej.skrabec@siol.net