drm: bridge: Detach bridge from encoder at encoder cleanup time

Most drivers that use bridges forgot to detach them at cleanup time.
Instead of fixing them one by one, detach the bridge in the core
drm_encoder_cleanup() function.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1481709550-29226-5-git-send-email-laurent.pinchart+renesas@ideasonboard.com