drm/amdgpu: change Vega IH ring 1 config

Disable overflow and enable full drain. This makes fault handling on ring 1
much more reliable since we don't generate back pressure any more.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>