drm: mali-dp: Add RGB writeback formats for DP550/DP650

Add a layer bit for the SE memory-write, and add it to the pixel format
matrix for DP550/DP650.

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
[rebased and fixed conflicts]
Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

drivers/gpu/drm/arm/malidp_hw.h

@@ -33,6 +33,7 @@ enum {
 	DE_GRAPHICS2 = BIT(2), /* used only in DP500 */
 	DE_VIDEO2 = BIT(3),
 	DE_SMART = BIT(4),
+	SE_MEMWRITE = BIT(5),
 };
 
 struct malidp_format_id {