drm/amd/display: handle active dongle port type is DP++ or DP case

[Why]:
Some active dongles have DP++ port and DP port at the same time. Current
code doesn't cover DP++ case and processes as default DVI case, in which
audio is disabled. Because of dual mode, DP case is also treat as DVI case
for the other port.

[How]:
According DP 1.4 spec, add DP++ procedure similar with HDMI case. Also
add None dongle type for DP case.

Signed-off-by: Dale Zhao <dale.zhao@amd.com>
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/include/dpcd_defs.h

@@ -43,7 +43,7 @@ enum dpcd_revision {
 enum dpcd_downstream_port_type {
 	DOWNSTREAM_DP = 0,
 	DOWNSTREAM_VGA,
-	DOWNSTREAM_DVI_HDMI,
+	DOWNSTREAM_DVI_HDMI_DP_PLUS_PLUS,/* DVI, HDMI, DP++ */
 	DOWNSTREAM_NONDDC /* has no EDID (TV,CV) */
 };