drm/sun4i: Fix DE2 mixer size

DE2 mixer is always 0x6000 bytes in size on all known SoCs.

While at it, introduce a macro for that.
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/20181104182705.18047-11-jernej.skrabec@siol.net

drivers/gpu/drm/sun4i/sun8i_mixer.c

@@ -460,7 +460,7 @@ static int sun8i_mixer_bind(struct device *dev, struct device *master,
 	base = sun8i_blender_base(mixer);
 
 	/* Reset the registers */
-	for (i = 0x0; i < 0x20000; i += 4)
+	for (i = 0; i < DE2_MIXER_UNIT_SIZE; i += 4)
 		regmap_write(mixer->engine.regs, i, 0);
 
 	/* Enable the mixer */

drivers/gpu/drm/sun4i/sun8i_mixer.h

@@ -29,6 +29,8 @@
 
 #define SUN8I_MIXER_GLOBAL_DBUFF_ENABLE		BIT(0)
 
+#define DE2_MIXER_UNIT_SIZE			0x6000
+
 #define DE2_BLD_BASE				0x1000
 #define DE2_CH_BASE				0x2000
 #define DE2_CH_SIZE				0x1000