drm/ttm: Reorder sys manager cleanup step

drm/ttm: Reorder sys manager cleanup step

With the current cleanup flow, we could trigger a NULL pointer
dereference if there is a delayed destruction of a BO with a
system resource that gets executed on drain_workqueue() call,
as we attempt to free a resource using an already released
resource manager.

Remove the device from the device list and drain its workqueue
before releasing the system domain manager in ttm_device_fini().

Signed-off-by: Karolina Stolarek <karolina.stolarek@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231016121525.2237838-1-karolina.stolarek@intel.com
Signed-off-by: Christian König <christian.koenig@amd.com>