dt-bindings: display/msm: Add SM6375 DSI PHY

SM6375 has a single 7nm DSI PHY. Document it.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/518509/
Link: https://lore.kernel.org/r/20230116114059.346327-1-konrad.dybcio@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>