dt-bindings: thermal: rcar-thermal: Add device tree support for r8a7742

Add thermal sensor support for r8a7742 SoC. The Renesas RZ/G1H
(r8a7742) thermal sensor module is identical to the R-Car Gen2 family.

No driver change is needed due to the fallback compatible value
"renesas,rcar-gen2-thermal".

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marian-Cristian Rotariu <marian-cristian.rotariu.rb@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rob Herring <robh@kernel.org>