drm/udl: Unplugging a device now unregisters it

drm/udl: Unplugging a device now unregisters it

Rather than manually perform our unregistration actions before shutting
down the device, move them to drm_unplug_dev().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
Cc: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466778982-6974-4-git-send-email-chris@chris-wilson.co.uk