dt-bindings: thermal: rockchip: Tighten grf requirements

dt-bindings: thermal: rockchip: Tighten grf requirements

Instead of having an optional rockchip,grf property, forbid using it on
platforms without registers in a GRF being needed for thermal monitoring
and make it mandatory on the platforms actually needing it.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250820-thermal-rockchip-grf-warning-v2-3-c7e2d35017b8@kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>