ARM: dts: Include R-Car Gen2 product name in DTSI files

Improve the user friendliness of the DTS code base by including the
R-Car product name in each R-Car Gen2 DTSI file.

The product names are taken from:
Documentation/devicetree/bindings/arm/shmobile.txt
Signed-off-by: Magnus Damm <damm@opensource.se>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7790.dtsi

 // SPDX-License-Identifier: GPL-2.0
 /*
- * Device Tree Source for the r8a7790 SoC
+ * Device Tree Source for the R-Car H2 (R8A77900) SoC
  *
  * Copyright (C) 2015 Renesas Electronics Corporation
  * Copyright (C) 2013-2014 Renesas Solutions Corp.

arch/arm/boot/dts/r8a7791.dtsi

 // SPDX-License-Identifier: GPL-2.0
 /*
- * Device Tree Source for the r8a7791 SoC
+ * Device Tree Source for the R-Car M2-W (R8A77910) SoC
  *
  * Copyright (C) 2013-2015 Renesas Electronics Corporation
  * Copyright (C) 2013-2014 Renesas Solutions Corp.

arch/arm/boot/dts/r8a7792.dtsi

 // SPDX-License-Identifier: GPL-2.0
 /*
- * Device Tree Source for the r8a7792 SoC
+ * Device Tree Source for the R-Car V2H (R8A77920) SoC
  *
  * Copyright (C) 2016 Cogent Embedded Inc.
  */

arch/arm/boot/dts/r8a7793.dtsi

 // SPDX-License-Identifier: GPL-2.0
 /*
- * Device Tree Source for the r8a7793 SoC
+ * Device Tree Source for the R-Car M2-N (R8A77930) SoC
  *
  * Copyright (C) 2014-2015 Renesas Electronics Corporation
  */

arch/arm/boot/dts/r8a7794.dtsi

 // SPDX-License-Identifier: GPL-2.0
 /*
- * Device Tree Source for the r8a7794 SoC
+ * Device Tree Source for the R-Car E2 (R8A77940) SoC
  *
  * Copyright (C) 2014 Renesas Electronics Corporation
  * Copyright (C) 2014 Ulrich Hecht