drm/amdgpu: assign VM invalidation engine manually v2

For Vega10 we have 18 VM invalidation engines for each VMHUB.

Start to assign them manually to the rings.

v2: add a BUG_ON if we use to many engines

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>