drm/amdgpu: apply gfx_v8 fixes to gfx_v7 as well

We never ported that back to CIK, so we could run into VM faults here.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org