arm64: dts: renesas: Include R-Car product name in DTSI files

Browsing the DTS for all the R-Car SoCs with similar part numbers
makes my head hurt, so to improve the user friendliness of the
DTS code base include R-Car product name in each DTSI file.

Product names are derived from
Documentation/devicetree/bindings/arm/shmobile.txt

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>