The gfxhub and mmhub code are now helpers for gmc rather
than standalone IPs.  When that changes these were left
over.  Remove them.
Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>