drm/amd/display: Added power down on boot for DCN3

drm/amd/display: Added power down on boot for DCN3

[Why]
The change of setting a timer callback on boot for 10 seconds is still
working, just lost power down on boot and power down for DCN3.

[How]
Added power down on boot and power down for DCN3.

Reviewed-by: Anthony Koo <anthony.koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Derek Lai <Derek.Lai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>