drm/sun4i: Add support for H6 DW HDMI controller

H6 has DW HDMI 2.0b controller v2.12a.

It supports 4K at 60 Hz and HDCP 2.2.

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/20181104182705.18047-20-jernej.skrabec@siol.net