drm/amdgpu: add 1.3.1/2.4.0 athub CG support

This patch adds 1.3.1/2.4.0 athub clock gating support.

Signed-off-by: Aaron Liu <aaron.liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>