drm/ttm: rework BO delayed delete. v2

drm/ttm: rework BO delayed delete. v2

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/