dt-bindings: mmc: sdhci-msm: Document the SM8550 compatible

Document the compatible for SDHCI on SM8550.

Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
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-sdhci-v1-0-797864a30e71@linaro.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>