drm/amdgpu: more scheduler cleanups v2

Embed the scheduler into the ring structure instead of allocating it.
Use the ring name directly instead of the id.

v2: rebased, whitespace cleanup

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: Chunming <Zhou&lt;david1.zhou@amd.com>