drm/amdgpu: fix "use bulk moves for efficient VM LRU handling" v2

First step to fix the LRU corruption, we accidentially tried to move things
on the LRU after dropping the lock.

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