Revert D30745960: [DDP] Remove SPMD from self.modules_buffers
Test Plan: revert-hammer
Differential Revision:
D30745960 (https://github.com/pytorch/pytorch/commit/15532595209d2daf34d35e10f8d3d3b64966aea2)
Original commit changeset: 66a8f9847e9f
fbshipit-source-id: d3f3fb813c45ac1b0ff15c6154b2e99e5dbab433
