dt-bindings: gpu: Convert Samsung Image Scaler to dt-schema

Convert Samsung Image Scaler to newer dt-schema format.

Signed-off-by: Maciej Falkowski <m.falkowski@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>