dt-bindings: thermal: rcar: Add device tree support for r8a7744

Add thermal sensor support for r8a7744 SoC. The Renesas RZ/G1N
(r8a7744) 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: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>