drm/sun4i: Introduce color encoding and range properties

In order to correctly convert YUV color space to RGB, we have to know
color encoding and range.

Introduce these two properties using helper method.

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/20190713120346.30349-2-jernej.skrabec@siol.net