drm/amd/display: Use 1/8th DSC target bitrate precision for N4:2:2 and 4:2:0 formats

[why]
On at least some of the devices (e.g. Realtek scaler) we get a black screen if 1/16th
precision is used.

[how]
Work around it by reducing precision to 1/8th for N4:2:2 and 4:2:0 color formats. This
is a safe workaround and would have a very mild impact on the quality.
The issue is still to be root-caused and fixed correctly.
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c

@@ -228,6 +228,10 @@ static bool dc_intersect_dsc_caps(
 
 	dsc_common_caps->bpp_increment_div = min(dsc_sink_caps->bpp_increment_div, dsc_enc_caps->bpp_increment_div);
 
+	// TODO DSC: Remove this workaround for N422 and 420 once it's fixed, or move it to get_dsc_encoder_caps()
+	if (pixel_encoding == PIXEL_ENCODING_YCBCR422 || pixel_encoding == PIXEL_ENCODING_YCBCR420)
+		dsc_common_caps->bpp_increment_div = min(dsc_common_caps->bpp_increment_div, (uint32_t)8);
+
 	return true;
 }