drm/amdgpu: add spin lock to protect freed list in vm (v2)

there is a protection fault about freed list when OCL test.
add a spin lock to protect it.

v2: drop changes in vm_fini

Signed-off-by: JimQu <jim.qu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -956,6 +956,8 @@ struct amdgpu_vm {
 	struct amdgpu_vm_id	ids[AMDGPU_MAX_RINGS];
 	/* for interval tree */
 	spinlock_t		it_lock;
+	/* protecting freed */
+	spinlock_t		freed_lock;
 };
 
 struct amdgpu_vm_manager {