dt-bindings: thermal: rcar-gen3-thermal: Add r8a774e1 support

Document RZ/G2H (R8A774E1) SoC bindings.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1594811350-14066-3-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com