arm64: dts: qcom: sm8450: Add GPI DMA compatible fallback

Use SM6350 as fallback for GPI DMA, to indicate devices are compatible
and that drivers can bind with only one compatible.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>