drm/sun4i: Add basic support for DE3

Display Engine 3 is an upgrade of DE2 with new features like support for
10 bit color formats and support for AFBC.

Most of DE2 code works with DE3, except some small details.

Implement basic support for DE3. Support for 10 bit colort formats and
AFBC, among others missing features, will be added later.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/260238/