This patch reworks the whole delayed deletion of BOs which aren't idle.

Instead of having two counters for the BO structure we resurrect the BO
when we find that a deleted BO is not idle yet.

This has many advantages, especially that we don't need to
increment/decrement the BOs reference counter any more when it
moves on the LRUs.

v2: remove duplicate ttm_tt_destroy, fix holde lock for LRU move
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: xinhui pan <xinhui.pan@amd.com>
Link: https://patchwork.freedesktop.org/patch/352912/