drm/ttm: optimize ttm_mem_evict_first v5

drm/ttm: optimize ttm_mem_evict_first v5

Deleted BOs with the same reservation object can be reaped even if they
can't be reserved.

v2: rebase and we still need to remove/add the BO from/to the LRU.
v3: fix remove/add one more time, cleanup the logic a bit
v4: we should still check if the eviction is valuable
v5: add comment suggested by Michel

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-and-Tested-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>