drm/msm/dpu: Add UBWC support for RGB8888 formats

Hardware only natively supports BGR8888 UBWC.
UBWC support for RGB8888 can be had by pretending
that the buffer is BGR.

Signed-off-by: Fritz Koenig <frkoenig@google.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rob Clark <robdclark@chromium.org>