dt-bindings: dma: qcom: gpi: add compatible for sm8550

The Qualcomm SM8550 uses GPI DMA for its GENI interface. Add a compatible
string for it in the documentation by using the SM6350 as fallback.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221114-narmstrong-sm8550-upstream-gpi-v1-0-33b28a227c5d@linaro.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>