drm/ttm: add back a reference to the bdev to the res manager

It is simply a lot cleaner to have this around instead of adding
the device throughout the call chain.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220124122514.1832-3-christian.koenig@amd.com