dt-bindings: thermal: rcar-thermal: Improve schema validation

- Factor out common required properties,
  - "interrupts", "clocks", and "power-domains" are required on R-Mobile
    APE6, too,
  - Invert logic to simplify descriptions.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201028153541.1736279-1-geert+renesas@glider.be