drm/sun4i: Disable unused DE2 sub-engines

Some sub-engines are unused. Disable them explicitly.

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/20181104182705.18047-12-jernej.skrabec@siol.net