drm/amdgpu: enable IH ring 1 and ring 2 v4

The entries are ignored for now, but it at least stops crashing the
hardware when somebody tries to push something to the other IH rings.

v2: limit ring size, add TODO comment
v3: only program rings if they are actually allocated
v4: limit the ring init to Vega10

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>