drm/ttm: fix busy memory to fail other user v10

BOs on the LRU might be blocked during command submission
and cause OOM situations.

Avoid this by blocking for the first busy BO not locked by
the same ticket as the BO we are searching space for.

v10: completely start over with the patch since we didn't
     handled a whole bunch of corner cases.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Tested-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>