drm: renesas: shmobile: Shutdown the display on remove

When the device is unbound from the driver, the display may be active.
Make sure it gets shut down.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/ddf2736459d59d0e961f240e77da7b0a28caae15.1694767209.git.geert+renesas@glider.be