drm/sun4i: Add DE2 CSC library

DE2 have many CSC units - channel input CSC, channel output CSC and
mixer output CSC and maybe more.

Fortunately, they have all same register layout, only base offsets
differs.

Add support only for channel output CSC for now.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171201060550.10392-24-jernej.skrabec@siol.net