drm/amd/display: Add OTG check for set AV mute

drm/amd/display: Add OTG check for set AV mute

[Why && How]
OTG can be disabled before setting dpms on. Add check to skip wait
when setting AV mute if OTG is disabled.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>