drm/amdgpu: remove re-route ih in psp v12

APU doesn't have second IH ring, so re-routing action here is a no-op.
It will take a lot of time to wait timeout from PSP during the
initialization. So remove the function in psp v12.

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