drm/amd/display: Control power gating by driver.

[Why]
This disablement would be specific for Nav10 and shouldn’t be propagated to the other programs.

[How]
Power gating is controlled by driver.

Signed-off-by: JinZe.Xu <JinZe.Xu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>