drm/msm/dpu: drop DPU_DIM_LAYER from MIXER_MSM8998_MASK

The msm8998 doesn't seem to support DIM_LAYER, so drop it from
the supported features mask.

Fixes: 2d8a4edb ("drm/msm/dpu: use feature bit for LM combined alpha check")
Fixes: 94391a14

 ("drm/msm/dpu1: Add MSM8998 to hw catalog")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/522231/
Link: https://lore.kernel.org/r/20230211231259.1308718-12-dmitry.baryshkov@linaro.org
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>