drm/mali-dp: Add RGB writeback formats for DP500.

Annotate the pixel format matrix for DP500 with the memory-write flag
for formats that are supported by the SE memwrite engine.

Reviewed-by: Brian Starkey <brian.starkey@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
1 file changed