drm/sun4i: csc: Rework DE3 CSC macros

Rework DE3 CSC macros to take just one coordinate instead of two. This
will make its usage easier in subsequent commit.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20210110201947.3611649-2-jernej.skrabec@siol.net