drm/mediatek: add RGB color format support for RDMA

This patch add RGB color format support for RDMA,
including RGB565, RGB888, RGBA8888 and ARGB8888.

Signed-off-by: Stu Hsieh <stu.hsieh@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>