drm/amd/display: add DalEnableHDMI20 key support

[why]
"DalEnableHDMI20" set to 0, disallow HDMI YCbCr420 and  pixel clock > 340Mhz
Default is enabled.
Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc.h

@@ -251,6 +251,7 @@ struct dc_debug {
 	bool recovery_enabled;
 	bool avoid_vbios_exec_table;
 	bool scl_reset_length10;
+	bool hdmi20_disable;
 
 };
 struct dc_state;

drivers/gpu/drm/amd/display/dc/dce/dce_link_encoder.c

@@ -646,6 +646,9 @@ static bool dce110_link_encoder_validate_hdmi_output(
 	if (!enc110->base.features.flags.bits.HDMI_6GB_EN &&
 		adjusted_pix_clk_khz >= 300000)
 		return false;
+	if (enc110->base.ctx->dc->debug.hdmi20_disable &&
+		crtc_timing->pixel_encoding == PIXEL_ENCODING_YCBCR420)
+		return false;
 	return true;
 }
 
@@ -773,6 +776,9 @@ void dce110_link_encoder_construct(
 				__func__,
 				result);
 	}
+	if (enc110->base.ctx->dc->debug.hdmi20_disable) {
+		enc110->base.features.flags.bits.HDMI_6GB_EN = 0;
+	}
 }
 
 bool dce110_link_encoder_validate_output_with_stream(

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_link_encoder.c

@@ -596,6 +596,9 @@ static bool dcn10_link_encoder_validate_hdmi_output(
 	if (!enc10->base.features.flags.bits.HDMI_6GB_EN &&
 		adjusted_pix_clk_khz >= 300000)
 		return false;
+	if (enc10->base.ctx->dc->debug.hdmi20_disable &&
+		crtc_timing->pixel_encoding == PIXEL_ENCODING_YCBCR420)
+		return false;
 	return true;
 }
 
@@ -728,6 +731,9 @@ void dcn10_link_encoder_construct(
 				__func__,
 				result);
 	}
+	if (enc10->base.ctx->dc->debug.hdmi20_disable) {
+		enc10->base.features.flags.bits.HDMI_6GB_EN = 0;
+	}
 }
 
 bool dcn10_link_encoder_validate_output_with_stream(