drm/display/dp: Assume 8 bpc support when DSC is supported

As per DP v1.4, a DP DSC Sink device shall support 8bpc in DPCD 6Ah.
Apparently some panels that do support DSC, are not setting the bit for
8bpc.

So always assume 8bpc support by DSC decoder, when DSC is claimed to be
supported.

v2: Use helper to get check dsc support. (Ankit)
v3: Fix styling and other typos. (Jani)
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230824125121.840298-2-ankit.k.nautiyal@intel.com

drivers/gpu/drm/display/drm_dp_helper.c

@@ -2449,12 +2449,16 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S
 	int num_bpc = 0;
 	u8 color_depth = dsc_dpcd[DP_DSC_DEC_COLOR_DEPTH_CAP - DP_DSC_SUPPORT];
 
+	if (!drm_dp_sink_supports_dsc(dsc_dpcd))
+		return 0;
+
 	if (color_depth & DP_DSC_12_BPC)
 		dsc_bpc[num_bpc++] = 12;
 	if (color_depth & DP_DSC_10_BPC)
 		dsc_bpc[num_bpc++] = 10;
-	if (color_depth & DP_DSC_8_BPC)
-		dsc_bpc[num_bpc++] = 8;
+
+	/* A DP DSC Sink device shall support 8 bpc. */
+	dsc_bpc[num_bpc++] = 8;
 
 	return num_bpc;
 }