ARM: dts: rzg1: Add reset control properties for display

Add reset control properties to the devices node for the Display Units
on all supported RZ/G1 SoCs.  Note that on these SoCs, there is only a
single reset for all DU channels.

Join the clocks lines while at it, to increase uniformity.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20200218133019.22299-3-geert+renesas@glider.be