drm/msm/dpu: fix writeback programming for YUV cases

For YUV cases, setting the required format bits was missed
out in the register programming. Lets fix it now in preparation
of adding YUV formats support for writeback.

changes in v2:
    - dropped the fixes tag as its not a fix but adding
      new functionality

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/571814/
Link: https://lore.kernel.org/r/20231212205254.12422-4-quic_abhinavk@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>