drm/amd/display: Set/Reset avmute when disable/enable stream

[Why]
When disconnect fe from be, something such as unstable clock may cause
garbage occurs.

[How]
Send set avmute at the beginning of disable stream and send reset avmute
at the end of enable stream.

Signed-off-by: Jinze Xu <jinze.xu@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>