drm/amd/display: Fix noise issue on HDMI AV mute

[Why]
When mode switching is triggered there is momentary noise visible on
some HDMI TV or displays.

[How]
Wait for 2 frames to make sure we have enough time to send out AV mute
and sink receives a full frame.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Leo Ma <hanghong.ma@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>