drm/sun4i: Add a DRC driver

The A33 pipeline also has a component called DRC. Even though its exact
features and programming model is not known (or documented), it needs to
be clocked for the pipeline to carry the video signal all the way.

Add a minimal driver for it that just claim the needed resources for the
pipeline to operate properly.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Peter Korsgaard <peter@korsgaard.com>