ARM: dts: r8a7745: Convert to new DU DT bindings

The DU DT bindings have been updated to drop the reg-names property.
Update the r8a7745 device tree accordingly.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20200218132217.21454-1-geert+renesas@glider.be