drm/amdgpu/gfx9: allocate queues horizontally across pipes

Pipes provide better concurrency than queues, therefore we want to make
sure that apps use queues from different pipes whenever possible.

Optimize for the trivial case where an app will consume rings in order,
therefore we don't want adjacent rings to belong to the same pipe.

gfx9 was missed when these patches were rebased.

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