dt-bindings: thermal: rcar-gen3-thermal: add r8a77965

Based on previous work by Ryo Kataoka <ryo.kataoka.wt@renesas.com>.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>