drm/sun4i: Add A83T support

Add support for the A83T display pipeline.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/614b430adf3a67320362a75c01b01bd53013da8a.1513854122.git-series.maxime.ripard@free-electrons.com