drm/amd/display: Revert "drm/amd/display: allow edp updates for virtual signal"

This reverts commit 4ad3ee5.

[WHY & HOW]
Virtual signal is not supported as audio capable by DC.

Reviewed-by: Chao-kai Wang <stylon.wang@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Alex Hung

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

@@ -132,7 +132,6 @@ static inline bool dc_is_audio_capable_signal(enum signal_type signal)
 {
 	return (signal == SIGNAL_TYPE_DISPLAY_PORT ||
 		signal == SIGNAL_TYPE_DISPLAY_PORT_MST ||
-		signal == SIGNAL_TYPE_VIRTUAL ||
 		dc_is_hdmi_signal(signal));
 }