drm/amd/display: Added power down for DCN10

drm/amd/display: Added power down for DCN10

[Why]
The change of setting a timer callback on boot for 10 seconds is still
working, just lacked power down for DCN10.

[How]
Added power down for DCN10.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
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>