Revert "drm/bridge: Fix a NULL pointer dereference in drm_atomic_bridge_chain_check()"

This reverts commit b18398c1 ("drm/bridge: Fix a NULL pointer
dereference in drm_atomic_bridge_chain_check()"). Commit 6ed7e962


("drm/bridge: Add a drm_bridge_state object") introduced a circular
dependency between drm.ko and drm_kms_helper.ko which uncovered a
misdesign in how the whole thing was implemented. Let's revert all
patches depending on the bridge_state infrastructure for now.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200107185807.606999-2-boris.brezillon@collabora.com