drm: Rename drm_connector_unplug_all() to drm_connector_unregister_all()

drm: Rename drm_connector_unplug_all() to drm_connector_unregister_all()

Current name is a bit misleading because what that helper function
really does it calls drm_connector_unregister() for all connectors.

This all has nothing to do with hotplugging so let's name things
properly.

And while at it remove potentially dangerous locking around
drm_connector_unregister() in rcar_du_remove() as mentioned
in kerneldoc for drm_connector_unregister_all().

Signed-off-by: Alexey Brodkin <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Boris Brezillon <[email protected]>
Cc: [email protected]
Acked-by: Laurent Pinchart <[email protected]>
Acked-by: Boris Brezillon <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]