ARM: dts: rcar-gen2: Convert to new DU DT bindings

The DU DT bindings have been updated to drop the reg-names property.
Update the r8a7792 and r8a7794 device trees accordingly.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7792.dtsi

@@ -829,7 +829,6 @@ jpu: jpeg-codec@fe980000 {
 		du: display@feb00000 {
 			compatible = "renesas,du-r8a7792";
 			reg = <0 0xfeb00000 0 0x40000>;
-			reg-names = "du";
 			interrupts = <GIC_SPI 256 IRQ_TYPE_LEVEL_HIGH>,
 				     <GIC_SPI 268 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&cpg CPG_MOD 724>,

arch/arm/boot/dts/r8a7794.dtsi

@@ -1349,7 +1349,6 @@ fdp1@fe940000 {
 		du: display@feb00000 {
 			compatible = "renesas,du-r8a7794";
 			reg = <0 0xfeb00000 0 0x40000>;
-			reg-names = "du";
 			interrupts = <GIC_SPI 256 IRQ_TYPE_LEVEL_HIGH>,
 				     <GIC_SPI 268 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&cpg CPG_MOD 724>, <&cpg CPG_MOD 723>;