drm/amdgpu: don't create ih ring 1 and ring 2 for APU

APUs don't support ih ring 1 and ring 2.

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>