drm/amdgpu: prefer VMIDs idle on the current ring

Prefer to use a VMIDs which are idle on the ring we want to submit to. This
also removes bubbling idle VMIDs up on the LRU, which is actually not
beneficial.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
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>