drm/amd/powerplay: enable/disable auto thermal throttle for tonga.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Acked-by: Flora Cui <Flora.Cui@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>