drm: renesas: shmobile: Convert to use devm_request_irq()

Convert to managed IRQ handling, to simplify cleanup.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/8d870bdc59dd5e2754542388a03095ea09c96297.1694767209.git.geert+renesas@glider.be