drm/msm/dpu: Only enable DSC_MODE_MULTIPLEX if dsc_merge is enabled

When the topology calls for two interfaces on the current fixed topology
of 2 DSC blocks, or uses 1 DSC block for a single interface (e.g. SC7280
with only one DSC block), there should be no merging of DSC output.

This is already represented by the return value of
dpu_encoder_use_dsc_merge(), but not yet used to correctly configure
this flag.

Fixes: 58dca98 ("drm/msm/disp/dpu1: Add support for DSC in encoder")
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/577067/
Link: https://lore.kernel.org/r/20240204-dpu-dsc-multiplex-v1-1-080963233c52@somainline.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c

@@ -1860,7 +1860,9 @@ static void dpu_encoder_prep_dsc(struct dpu_encoder_virt *dpu_enc,
 	dsc_common_mode = 0;
 	pic_width = dsc->pic_width;
 
-	dsc_common_mode = DSC_MODE_MULTIPLEX | DSC_MODE_SPLIT_PANEL;
+	dsc_common_mode = DSC_MODE_SPLIT_PANEL;
+	if (dpu_encoder_use_dsc_merge(enc_master->parent))
+		dsc_common_mode |= DSC_MODE_MULTIPLEX;
 	if (enc_master->intf_mode == INTF_MODE_VIDEO)
 		dsc_common_mode |= DSC_MODE_VIDEO;